Variants of plasminogen and plasmin

ABSTRACT

The invention relates to variants of plasminogen and plasmin comprising one or more point mutations in the catalytic domain which reduce or prevent autocatylic destruction of the protease activity of plasmin. Compositions, uses and methods of using said variants of plasminogen and plasmin are also disclosed.

FIELD OF THE INVENTION

The invention relates to variants of plasminogen and plasmin comprising one or more point mutations in the catalytic domain which reduce or prevent autocatylic destruction of the protease activity of plasmin. Compositions, uses and methods of using said variants of plasminogen and plasmin are also disclosed.

BACKGROUND TO THE INVENTION

Activation of the zymogen plasminogen results in the formation of the fibrinolytically/thrombolytically active serine proteinase plasmin. Activation of endogenous plasminogen can be triggered or enhanced by the administration of a plasminogen activator such as urokinase, streptokinase, staphylokinase or tPA, or any variant thereof. Upon activation, the plasminogen protein is proteolytically cleaved into a heavy chain comprising the 5 kringle domains and a light chain comprising the catalytic domain. Both chains are held together via 2 disulfide bonds. After activation, an autolytic cleavage removes an N-terminal segment from the heavy chain (78 amino acids of human plasmin; 77 amino acids of bovine plasmin) and the bovine plasmin heavy chain can be further autocatalytically cleaved between kringles 3 and 4, hence giving rise to bovine midiplasmin (Christensen et al. 1995, Biochem J 305, 97-102). Activation of plasminogen to plasmin, triggered by the cleavage of the R561—V562 peptide bond in human plasminogen, induces a large conformational change in the light chain, said change resulting in the priming, or activation, of the catalytic triad within said light chain. Bacterial plasminogen activators such as streptokinase and staphylokinase form a complex with plasminogen and, without cleavage of the R561—V562 peptide bond of plasminogen, the catalytic site of plasminogen is activated due to conformational changes upon activator-plasminogen complex formation (plasminogen activation mechanisms are summarized in, e.g., the Introduction section of Terzyan et al. 2004; Proteins 56: 277-284).

Whereas plasminogen activators act as indirect thrombolytic agents, it has alternatively been suggested to use plasmin itself as a direct fibrinolytic/thrombolytic agent. Such direct use is, however, hampered by the fact that plasmin is, like many proteases, subject to autocatalytic proteolytic degradation which follows second order kinetics subject to product inhibition (Jespersen et al. 1986, Thrombosis Research 41, 395-404).

In the early 1960's it was established that plasmin can be stabilized at acidic pH, or alternatively at neutral pH provided an amino acid such as lysine is present. Nevertheless, autolytic cleavage after Lys104, Arg189 and Lys622 (numbering relative to Lys-plasmin) were reported even when plasmin is stored at pH 3.8 (WO01/36608). When plasmin is stored at the even lower pH of 2.2, non-autolytic acid cleavage occurs between Asp-Pro (D-P) at positions Asp62, Asp154 and Asp346 (WO01/36608). This illustrates that pH can be lowered to a point where no apparent autocatylic degradation occurs anymore but at which acid hydrolysis is becoming a factor of destabilization. No information is present in WO01/36608 as to which peptide bonds in plasmin are vulnerable to (autocatalytic) hydrolysis at neutral pH. Known stabilizers of plasmin include glycerol, sufficiently high ionic strength, fibrinogen and ε-aminocaproic acid (EACA), as disclosed by Jespersen et al. (1986, Thromb Res 41, 395-404). Lysine and lysine-derivatives (such as EACA and tranexamic acid) and p-aminomethylbenzoic acid (PAMBA) are some further known stabilizers (Uehsima et al. 1996, Clin Chim Acta 245, 7-18; Verstraete 1985, Drugs 29, 236-261). U.S. Pat. No. 4,462,980 reported on the formation of plasmin aggregates contributing to plasmin degradation despite storage at acidic conditions. A solution to this problem was provided in U.S. Pat. No. 4,462,980 by means of adding a polyhydroxy compound. Other ways of stabilizing plasmin include the addition of oligopeptidic compounds (e.g. U.S. Pat. No. 5,879,923). Alternatively, the catalytic site of plasmin can be reversibly blocked by means of derivatization, e.g. acylation (EP 0009879). Pegylation of plasmin has also been suggested as a means to stabilize the enzyme (WO 93/15189).

A number of plasmin variants other than truncated forms of plasmin have been described and include a chimeric microplasmin (WO 2004/045558) and variants with a point mutation at the two-chain cleavage site (U.S. Pat. No. 5,087,572) or at a catalytic triad amino acid (Mhashilkar et al. 1993, Proc Natl Acad Sci USA 90, 5374-5377; Wang et al., 2001, J Mol Biol 295, 903-914). Wang et al. (1995, Protein Science 4, 1758-1767 and 1768-1779) reported an extensive series of microplasminogen mutants at amino acid positions 545, 548, 550, 555, 556, 558, 560-564, 585, 740 and 788. A double mutant wherein cysteines at amino acid positions 558 and 566 were substituted for serines was reported by Linde et al. (1998, Eur J Biochem 251, 472-479). Takeda-Shitaka et al. (1999, Chem Pharm Bull 47, 322-328) refer to a plasmin variant with reduced activity, the variation involving the substitution of alanine at amino acid position 601 to threonine. All amino acid positions referred to above are relative to Glu-plasminogen starting with Glu at amino acid position 1. A non-cleavable plasminogen variant (cleavage between heavy and light chain impaired) is described in WO 91/08297. Dawson et al. (1994, Biochemistry 33, 12042-12047) describe the reduced affinity for streptokinase of a Glu-plasminogen variant with a Glu instead of Arg at position 719 (R719E). Jespers et al. (1998, Biochemistry 37, 6380-6386) produced in an Ala-scan the series of phage-displayed microplasminogen single-site mutants H569A, R610A, K615A, D660A, Y672A, R712A, R719A, T782A, R789A, and found that arginine at position 719 is key for interaction with staphylokinase; the D660A mutant was not further characterized due to very low expression; only the R719A mutant was additionally produced in soluble form. None of the mutants showed a gross change in proteolytic activity (substrate S-2403). Jespers et al. (1998) also included an active site mutant S741A in their analysis; the crystal structure of this mutant is disclosed in Wang et al. (2000, J Mol Biol 295, 903-914). In further attempts to unravel the streptokinase/plasminogen interaction sites, Terzyan et al. (2004, Proteins 56, 277-284) reported a number of microplasminogen mutants (K698M, D740N, S741A) in an already mutated background (R561A), the latter prohibiting proteolytic activation of plasminogen and thus prohibiting formation of active microplasmin (which would complicate the study of the contact-activation mechanism of the streptokinase-microplasminogen complex). Terzyan et al. (2004) further mention an “inadvertent” triple mutant R561A/H569Y/K698M apparently functionally indifferent from the double mutant R561A/K698M. Wang et al. (2000, Eur J Biochem 267, 3994-4001), in studying streptokinase/plasmin(ogen) interaction, produced a set of microplasminogen (amino acids 530-791 of Glu-plasminogen) mutants in a Cys536Ala and Cys541 Ser background. These mutants include the R561A mutation as described above (Terzyan et al. (2004)) as well as R561A/K698G, R561A/K698A and R561A/K698Q double mutants. In the same C536A/C541S background, single K698G and K698A mutations were introduced also, of which the K698G was not characterized further due to difficulties with purification. The above studies aimed at obtaining a better understanding of the characteristics of the plasminogen/plasmin molecule and did not report any clinical usefulness or benefit or putative clinical advantages of the plasminogen/plasmin mutants. Peisach et al. (1999, Biochemistry 38, 11180-11188) succeeded in determining the crystal structure of microplasminogen containing the M585Q, V673M and M788L mutations.

Nguyen & Chrambach (1981, Preparative Biochem 11, 159-172) reported the presence of “a minor and unidentified protein component” of 10.0 kDa based on reducing SDS-PAGE of a crude commercial preparation of urokinase-activated plasmin (Homolysin). The differences in autolysis of human plasmin depending on pH have been described in detail by Shi & Wu (1988, Thrombosis Research 51, 355-364). Ohyama et al. (2004, Eur J Biochem 271, 809-820) proposed the use of non-lysine analog plasminogen modulators in treatment of cancer due to the enhancement of plasmin autoproteolysis by such compounds which results in the enhanced formation of angiostatins (in the presence of the plasminogen activator urokinase). Table 3 of Ohyama et al. (2004) lists as many as 15 cleavage sites within plasmin subjected to autoproteolyis-enhancing compounds. In discussing their observations in view of prior investigations, it would seem that the autoproteolyis-enhancing compounds are more or less selectively enhancing proteolysis of the B/light-chain whereas minimum degradation of both A/heavy- and B-chain was found in the absence of the autoproteolyis-enhancing compounds.

It is clear that none of the above methods/variants solves the problem of providing a plasmin stabilized at the molecular level. The provision of a plasmin variant (or of a corresponding plasminogen variant from which plasmin can be derived) with a catalytic domain intrinsically resistant to autocatalytic degradation would be a significant step forward towards efficient and safe long-term storage as well as towards efficient and safe therapeutic use of plasmin such as in thrombolytic therapy or in the induction of posterior vitreous detachment or vitreous liquefaction in the eye.

SUMMARY OF THE INVENTION

The current invention relates to isolated plasminogen variants or plasmins obtained from it, or to isolated plasmin variants, or to proteolytically active or reversible inactive derivatives of any of said plasmins characterized in that said plasminogen or plasmin variants or said derivatives comprise in their catalytic domain the mutation of at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to autoproteolysis into an amino acid of which the peptide bond with internal amino acid at position P+1 is less or not prone to autoproteolysis.

Alternatively, the plasminogen variant, plasmin variant, or plasmin derivative according to the invention comprises in its catalytic domain the mutation of at least two internal amino acids at positions P and P′ of which the peptide bond with internal amino acids at positions P+1 and P′+1 are prone to autoproteolysis into amino acids of which the peptide bond with internal amino acids at positions P+1 and P′+1 is less or not prone to autoproteolysis.

In particular, said internal amino acids at positions P or P and P′ are lysines or arginines.

More specifically, said at least one or two internal amino acids at position P or at positions P and P′ may be at least one or at least two of:

-   (i) lysine at position 137 of the human plasmin catalytic domain, or     the corresponding lysine or arginine of a non-human plasmin     catalytic domain; -   (ii) lysine at position 147 of the human plasmin catalytic domain,     or the corresponding lysine or arginine of a non-human plasmin     catalytic domain; or -   (iii) arginine at position 158 of the human plasmin catalytic     domain, or the corresponding arginine or lysine of a non-human     plasmin catalytic domain;     wherein said human plasmin catalytic domain is starting with the     amino acid valine at position 1 which is the same valine amino acid     occurring at position 562 of human Glu-plasminogen.

Alternatively, said at least one internal amino acid at position P is the lysine at position 147 of the human plasmin catalytic domain, or is the corresponding lysine or arginine of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen. Optionally, the plasminogen variants, plasmin variants, or plasmin derivatives with a mutation of the lysine at position 147 of the human plasmin catalytic domain (or corresponding lysine or arginine of a non-human plasmin catalytic domain) may further comprise a mutation of the internal amino acids at positions 137 and/or 158 of the human catalytic domain or of the corresponding lysines and/or arginines of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.

In a further alternative, the plasminogen variants, plasmin variants, or plasmin derivatives according to the invention are such that:

-   (i) if the mutation of said at least one internal amino acid at     position P is the mutation of the lysine at position 137 of the     human plasmin catalytic domain (which is amino acid position 698     relative to human Glu-plasminogen) into an amino acid rendering the     peptide bond between amino acids 137 and 138 more resistant to     autoproteolysis, said plasminogen variant, plasmin variant or     plasmin derivative comprises an intact activation site at amino acid     positions 561 and 562 (relative to human Glu-plasminogen), and, when     amino acids at position 536 and 541 (relative to human     Glu-plasminogen) outside the catalytic domain are present, said     amino acids are the wild-type cysteines, or -   (ii) if the mutation of said at least one internal amino acid at     position P is the mutation of the arginine at position 158 of the     human plasmin catalytic domain (which is amino acid position 719     relative to human Glu-plasminogen) into an alanine or glutamate,     then at least one other internal amino acid of the human plasmin     catalytic domain at a position P′ of which the peptide bond with     internal amino acid at position P′+1 is prone to autoproteolysis is     mutated into an amino acid of which the peptide bond with internal     amino acid at position P′+1 is less or not prone to autoproteolysis.

The plasminogen variant, plasmin variant, or plasmin derivative according to (i) or (ii) above may further comprise a mutation of the internal amino acid at position 147 of the human catalytic domain or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.

Any of the plasminogen variants, plasmin variants, or plasmin derivatives according to the invention may be characterized further in that its autolysis constant is at most 95% of the autolysis constant of wildtype plasmin.

Any of the plasminogen variants, plasmin variants, or plasmin derivatives according to the invention may be characterized further in that the catalytic constant k_(cat) is in the range of 10% to 200% of the k_(cat) of wildtype plasmin.

Any of the plasminogen variants, plasmin variants, or plasmin derivatives according to the invention may be characterized further in that its autolysis constant is at most 95% of the autolysis constant of wildtype plasmin and its catalytic constant k_(cat) is in the range of 10% to 200% of the k_(cat) of wildtype plasmin.

Without imposing any limitation, any of the above plasminogen variants, plasmin variants, or plasmin derivatives according to the invention may be one of Glu-plasminogen or Glu-plasmin, Lys-plasminogen or Lys-plasmin, midiplasminogen or midiplasmin, miniplasminogen or miniplasmin, microplasminogen or microplasmin, deltaplasminogen or deltaplasmin

The invention further relates to the isolated plasminogen variants, plasmin variants, or plasmin derivatives according to the invention, or a combination of any thereof for use as a medicament.

The invention also relates to compositions comprising an isolated plasminogen variant, plasmin variant, or plasmin derivative according to the invention, or a combination of any thereof, and at least one of a pharmaceutically acceptable diluent, carrier or adjuvant. Such composition may optionally further comprise at least one of an anticoagulant, a thrombolytic agent, an anti-inflammatory agent, an antiviral agent, an antibacterial agent, an antifungal agent, an anti-angiogenic agent, an anti-mitotic agent, an antihistamine or an anaesthetic.

The invention also includes any beneficial application of an isolated plasminogen variant, plasmin variant, or plasmin derivative according to the invention. Without imposing any limitation, these include: inducing or promoting lysis of a pathological fibrin deposit in a subject, inducing posterior vitreous detachment in the eye and/or for inducing liquefaction of the vitreous in the eye, facilitating surgical vitrectomy in the eye in a subject, enzymatic debridement of injured tissue of a subject, reducing circulating fibrinogen in a subject, reducing α2-antiplasmin levels in a subject, reducing the risk of pathological fibrin deposition.

The invention further relates to methods for screening for an autoproteolytically stable plasmin variant, said methods comprising the steps of:

-   (i) identifying in the catalytic domain of wild-type plasmin at     least one internal amino acid at position P of which the peptide     bond with internal amino acid at position P+1 is prone to     autoproteolysis, -   (ii) mutating the amino acid at position P identified in (i) into an     amino acid of which the peptide bond with internal amino acid at     position P+1 is less or not prone to autoproteolysis, -   (iii) determining the autoproteolytic stability of the mutant     obtained from (ii), and -   (iv) selecting from (iii) a mutant that is autoproteolytically     stable as the autoproteolytically stable variant.

Alternatively, such methods for screening for an autoproteolytically stable plasmin variant may comprise the steps of:

-   (i) mutating one or more of the arginine or lysine amino acids at     positions 137, 147 and 158 of the human plasmin catalytic domain, or     of the corresponding arginines or lysines of a non-human plasmin,     into an amino acid different from the natural amino acid, -   (ii) determining the autoproteolytic stability of the mutant     obtained from (i), and -   (iii) selecting from (ii) a mutant that is autoproteolytically     stable as the autoproteolytically stable plasmin variant;     wherein said human plasmin catalytic domain is starting with the     amino acid valine at position which is the same valine amino acid     occurring at position 562 of human Glu-plasminogen.

Any of the above screening methods may optionally further comprise a step wherein the proteolytic activity of the autoproteolytically stable plasmin variant is determined.

The invention further includes methods for enhancing long-term storage stability of a plasmin-comprising composition, said methods comprising the step of identifying an autoproteolytically stable plasmin variant capable of being stored over a long time without significant loss of proteolytic activity.

The invention further includes methods for producing a plasminogen variant according to the invention, said methods including the steps of:

-   (i) introducing a nucleic acid encoding a plasminogen according to     the invention in a suitable host cell capable of expressing said     plasminogen; -   (ii) growing the host cell obtained in (i) under conditions and     during a time sufficient for expression of said plasminogen in said     host cell; and -   (iii) harvesting the plasminogen expressed in (ii).

Such methods may optionally further include a step (iv) wherein the plasminogen harvested in (iii) is purified.

The invention likewise includes methods for producing a plasmin variant according to the invention, said methods including the steps of:

-   (i) introducing a nucleic acid encoding a plasminogen according to     the invention in a suitable host cell capable of expressing said     plasminogen; -   (ii) growing the host cell obtained in (i) under conditions and     during a time sufficient for expression of said plasminogen in said     host cell; -   (iii) harvesting the plasminogen expressed in (ii); -   (iv) activating the plasminogen of (iii) to plasmin.

Such methods may further optionally comprise a step wherein the plasminogen harvested in (iii) is purified prior to activation in (iv). Further, in any method for producing a plasmin variant according to the invention, the active plasmin obtained in (iv) may optionally be purified. Yet further, the active plasmin variant produced according to a method of the invention may optionally be derivatized and/or reversibly inactivated.

The invention further relates to isolated nucleic acid sequences encoding a plasminogen variant or plasmin variant according to the invention. Recombinant vectors comprising such nucleic acids are also part of the invention, as are host cells transformed with such nucleic acid or recombinant vector.

FIGURE LEGENDS

FIG. 1. Amino acid sequence with double numbering of the amino acid positions of wild-type human Glu-plasminogen (1 to 791) and of the plasmin catalytic domain (1 to 230, amino acid sequence and numbering in bold). Microplasminogen as used for demonstrating the invention starts at amino acid position 543 (numbering relative to Glu-plasminogen). The highlighted amino acids at amino acid positions 137, 147 and 158 (numbering relative to plasmin catalytic domain) were determined to be amino acids of which the peptide bond with amino acids at positions 138, 148 and 159, respectively, are sensitive to autocatalytic cleavage. Kringle domains (as derived from the information included in GenBank accession number AAA36451) are boxed and their amino acid sequences typed alternating in normal and italic letters. The catalytic triad amino acids are circled.

FIG. 2. Size exclusion chromatography (SEC) profile of large-scale produced microplasmin. The eluates corresponding to fraction number 5 (pre-peak 1), fraction numbers 7&8 (pre-peak 2), fraction numbers 10-12 (microplasmin peak), and fraction numbers 15&16 (post-peak) were collected and the material therein subjected to N-terminal amino acid sequencing (Edman degradation). The peak eluting around fraction numbers 17-18 corresponds to the buffer peak. AU: absorbance units.

FIG. 3. Reducing SDS-PAGE analysis of large-scale produced microplasmin. Lane 1: molecular weight ladder, with molecular weights indicated at the left. Lane 2: microplasminogen. Lane 3: microplasmin at pH 3.1. Lane 4: microplasmin at pH 4.0. Lane 5: microplasmin at pH 5.0. Lane 6: microplasmin at pH 6.0. Lane 7: microplasmin at pH 7.0. All samples (final protein concentration 0.6 mg/mL) were left for 4 hrs at 20° C. at the indicated pH and then frozen at −70° C. The gel was stained with Coomassie Brilliant Blue. μP1g=microplasminogen, μP1=plasmin, front=leading gel front.

FIG. 4. Microplasmin was incubated in a neutral-pH buffer, and samples were collected after the indicated times and analyzed by SDS-PAGE (A) or western-blot (B). Arrow “a” indicates the intact microplasmin, whereas arrows “b” and “c” indicate the ˜15 kDa and ˜10 kDa fragments, respectively, that are autocatalytically produced.

FIG. 5. The kinetics of microplasmin autolysis as assessed by western-blot (circles) corresponds to the loss of microplasmin activity (squares).

FIG. 6. (A) Microplasmin was diluted in PBS (squares) or in porcine eye vitreous (circles) to a final concentration of 1.53 μM, and residual concentration of active microplasmin was measured at various time points. (B) Porcine eye vitreous samples were collected at the indicated time points and analyzed by western blot. The arrow indicates a ˜15 kDa fragment.

FIG. 7. (A) Immuno-affinity chromatogram of the microplasmin variant Lys137Met (K137M) on an immobilized anti-microplasmin antibody. Collected elution fractions are numbered 1-11 above the X-axis (elution volume). (B) Reducing SDS-PAGE analysis of elution fractions of immune-affinity performed in (A). Lane 1: molecular weight ladder. Lane 2: eluate fraction 2. Lane 3: eluate fraction 3; Lane 4: eluate fraction 4; Lane 5: eluate fraction 5; Lane 6: eluate fraction 6; Lane 7: crude supernatant. The gel was Coomassie-stained.

FIG. 8. (A) Activation of the K137M variant with recombinant staphylokinase. Activity reached a maximum after 10 min (indicated by the arrow), then decreased as autolytic inactivation occurred. (B) Reducing SDS-PAGE of the K137M variant indicating that activation with staphylokinase is nearly complete within 10 min, and that loss of activity results from autolytic degradation, as evidenced by the accumulation two fragments of ˜17 and ˜8 kDa. Lanes 1-7 represent samples collected 0 min, 10 min, 1 h, 2 h, 3 h, 6 h and 24 h after addition of staphylokinase. (▴) Microplasminogen, (▾) microplasmin, (∇) autolytic degradation fragments. (C)HPLC analysis of samples collected 0 min, 10 min and 6 h after addition of staphylokinase. The HPLC profile obtained 10 min after addition of staphylokinase indicates that ˜85% of the inactive microplasminogen has been converted into the active microplasmin species, and the HPLC profile at t=6 h shows the presence of the autolytic degradation fragments (∇), in agreement with the SDS-gel showed in (B). The microplasmin peak area at t=10 min (arrow) was used to calculate the concentration of active species by comparison with a standard curve established with highly purified microplasmin (not shown). All HPLC data were obtained using an Acquity HPLC instrument (Waters). The microplasmin samples were typically diluted 5-fold in 0.1% Trifluoroacetic acid (TFA), 5% acetonitrile, and injected on a BEH300 C18 Acquity HPLC column (Waters) pre-equilibrated in 0.1% TFA, 34% acetonitrile. Elution was then performed with a 34 to 44% acetonitrile, 1.5-mL linear gradient in 0.1% TFA, and the proteins were detected by following the absorbance at 214 nm. The temperature of the column was maintained at 75° C., and all experiments were performed with a flow rate of 100 μL/min. (D) The quantification of the K137M microplasmin species at t=10 min by HPLC and the subsequent decrease in residual activity were combined to calculate the molar concentration of intact, active microplasmin present in the sample at each time point. The data were fitted with Equation 1 (see Example 3) to calculate the second order rate constant for autolysis (k). The open circles (◯) represent the data for the K137M variant. For comparative purposes, a similar set of data obtained with another variant (K147A-R158A) is also represented ().

FIG. 9. Determination of the kinetic parameters for the K137M microplasmin variant. Determination of k_(cat) and K_(m) from the measurement of initial rates of hydrolysis (v_(i)) at different substrate (S-2403) concentrations. The data were fitted with Equation 2 (see Example 4).

FIG. 10. Amino acid sequence alignment of mammalian plasminogen proteins retrieved from GenBank. The sequence alignment was run with the COBALT software (Constraint-based Multiple Alignment Tool; Papadopoulos & Agarwala, Bioinformatics 23:1073-79, 2007) available through the National Center for Biotechnology Information (NCBI) website with default settings. ▾: indication of start of Glu-plasminogen. The amino acid numbering is relative to human plasminogen.

DETAILED DESCRIPTION OF THE INVENTION

The current invention is based on the results of studying the mechanisms underlying the unforced auto-inactivation of the proteolytic activity of plasmin at neutral pH, a study for which the inventor chose to focus on microplasmin which consists mainly of the catalytic domain of plasmin. Peptide bonds susceptible to cleavage by plasmin are located at the C-terminus of lysine or arginine (Weinstein & Doolittle, 1972, Biochim Biophys Acta 258, 577-590). Nearly 10% (22 out of 230) of the amino acids of the plasmin catalytic domain (starting at amino acid position 562, a valine, in human Glu-plasminogen) are lysines or arginines. Theoretically all peptide bonds C-terminal of these lysines and arginines in one plasmin molecule can be proteolytically cleaved by another plasmin molecule.

One aspect of the invention thus relates to plasmin molecules and to plasminogen molecules, in particular plasminogen molecules that are activatable/can potentially be activated to plasmin, comprising in their catalytic domain one or more mutations of amino acids such that peptide bonds vulnerable to autoproteolytic degradation in wild-type plasmin or plasminogen are less or not vulnerable to autoproteolytic degradation in the plasmin and plasminogen molecules subject of the invention.

The invention in other words relates to an isolated plasminogen variant or plasmin obtained from it, or an isolated plasmin variant, or a proteolytically active or reversible inactive derivative of any of said plasmins, characterized in that said plasminogen variant or plasmin variant or derivative thereof is comprising in its catalytic domain the mutation of at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to (or sensitive to, susceptible to, or vulnerable to) autoproteolysis into an amino acid of which the peptide bond with internal amino acid at position P+1 is less or not prone (or less or not sensitive, susceptible, or vulnerable) to autoproteolysis. In particular, said internal amino acid at position P is a lysine or arginine. As reference used herein (unless stated otherwise), the catalytic domain of plasmin will be numbered relative to human plasmin, which is starting with the valine at position P=1 which is the same as the valine at position 562 of human Glu-plasminogen (see FIG. 1). Reference can also be made herein to two different amino acid positions in the plasmin catalytic domain, which are then termed P and P′, respectively.

Alternatively, the plasminogen variant, plasmin variant, or plasmin derivative according to the invention may comprise in its catalytic domain the mutation of at least two internal amino acids at position P and P′ of which the peptide bond with internal amino acids at positions P+1 and P′+1 are prone to autoproteolysis into amino acids of which the peptide bond with internal amino acids at position P+1 and P′+1 is less or not prone to autoproteolysis.

After having identified the amino acids at positions P, the person skilled in the art will be able to decide easily into which other amino acid the wild-type amino acid at position P can be mutated. Such decision may, but must not necessarily imply criteria such as amino acid size, amino acid charge, amino acid polarity, and/or amino acid hydropathy index (see Table 1). In particular for plasmin and plasminogen said internal amino acid at position P in all likelihood will be a lysine or arginine, implying that these should be mutated into an amino acid different from arginine or lysine, respectively. Moreover, the availability of the crystal structure of plasminogen and the plasmin catalytic domain (MMDB ID: 12717; PDB ID: 1DDJ; Wang et al., 2001, J Mol Biol 295, 903-914) is of great value in helping identifying the mutant amino acids such that the resulting mutant plasmin or plasminogen molecule retains proteolytic activity. Furthermore, it can be expected that mutation of a wild-type amino acid at said position P into either one of the amino acids of a given group will yield similar results. Based on Table 1, said given groups can be defined as follows:

-   -   hydrophobic aliphatic amino acids: Met, Ile, Leu and Val     -   hydrophobic aromatic amino acids: Phe     -   hydrophilic acidic amino acids: Asp, Glu, Asn and Gln     -   hydrophilic basic amino acids: Arg, Lys and H is     -   moderately hydrophobic aliphatic amino acids: Gly, Ala, Ser,         Thr, Cys, Pro     -   moderately hydrophobic aromatic amino acids: Tyr and Trp.

Of these, and for the purpose of mutation, Cys and Pro may be less favorable substitute amino acids of wild-type plasmin or plasminogen amino acids due to the creation of possible free thiol-group by a Cys, or due to more extensive disturbance of the protein structure by a Pro. Other amino acid substitutions include the mutation of a wild-type amino acid at said position P of a plasmin(ogen) catalytic domain into a non-natural or noncanonical amino acid, or into amino acid analogs, such as norleucine, norvaline, ornithine or citrulline (for more extensive list see, e.g., Hendrickson et al. 2004, Annu Rev Biochem 73, 147-176).

TABLE 1 Characteristics of amino acids. Side chain Side chain charge Hydropathy Amino Acid polarity (at pH 7) index Alanine Ala A nonpolar neutral 1.8 Arginine Arg R polar positive −4.5 Asparagine Asn N polar neutral −3.5 Aspartic acid Asp D polar negative −3.5 Cysteine Cys C nonpolar neutral 2.5 Glutamic acid Glu E polar negative −3.5 Glutamine Gln Q polar neutral −3.5 Glycine Gly G nonpolar neutral −0.4 Histidine His H polar positive −3.2 Isoleucine Ile I nonpolar neutral 4.5 Leucine Leu L nonpolar neutral 3.8 Lysine Lys K polar positive −3.9 Methionine Met M nonpolar neutral 1.9 Phenylalanine Phe F nonpolar neutral 2.8 Proline Pro P nonpolar neutral −1.6 Serine Ser S polar neutral −0.8 Threonine Thr T polar neutral −0.7 Tryptophan Trp W nonpolar neutral −0.9 Tyrosine Tyr Y polar neutral −1.3 Valine Val V nonpolar neutral 4.2

The inventor observed that, under the test conditions, only a limited number of autoproteolytic cleavages occur within the plasmin catalytic domain. As described in the Examples section, the current invention identified 3 hot spots of autoproteolysis. This, however, does not exclude the possibility for the existence of other peptide bonds that are autoproteolytically scissile.

Thus, in the above, said at least one internal amino acid at position P, or said at least two internal amino acids at positions P and P′, are more particularly at least one or at least two chosen from:

-   (i) lysine at position 137 of the human plasmin catalytic domain, or     the corresponding lysine or arginine of a non-human plasmin; -   (ii) lysine at position 147 of the human plasmin catalytic domain,     or the corresponding lysine or arginine of a non-human plasmin; or -   (iii) arginine at position 158 of the human plasmin catalytic     domain, or the corresponding lysine or arginine of a non-human     plasmin;     wherein said human plasmin catalytic domain is starting with the     amino acid valine at position 1 which is the same valine amino acid     occurring at position 562 of human Glu-plasminogen. To clarify the     amino acid numbering in human plasminogen and the human plasmin     catalytic domain, reference is made to FIG. 1 herein.

The identification of an amino acid in a non-human plasmin(ogen) sequence which “corresponds to” (i.e. the identification of a “corresponding” amino acid) an amino acid in the human plasmin(ogen) first implies the alignment of both amino acid sequences. Such alignment may require some optimization, such as introduction of minor gaps in one or both of the aligned sequences, to result in the highest identity and homology. Secondly, the amino acid in the non-human plasmin(ogen) aligning with the amino acid in the human plasmin(ogen) is identified and is herein referred to as the “corresponding” amino acid. FIG. 10 herein depicts such an alignment of publicly available mammalian plasminogen protein sequences, and highlights the amino acids of particular interest to the current invention in the human plasminogen sequence (line 1) together with the corresponding amino acids in the non-human plasminogen sequences (lines 2-18). The amino acids of particular interest are Lys at position 698 (position 137 in the catalytic domain, see FIG. 1), Lys at position 708 (position 147 in the catalytic domain, see FIG. 1) and Arg at position 719 (position 158 in the catalytic domain, see FIG. 1).

Said plasminogen variant, plasmin variant, or plasmin derivative according to the invention may be one wherein said at least one internal amino acid at position P is the lysine at position 147 of the human plasmin catalytic domain, or is the corresponding lysine or arginine of a non-human plasmin catalytic domain. It may optionally comprise further a mutation of the internal amino acids at positions 137 and/or 158 of the human catalytic domain or of the corresponding lysines and/or arginines of a non-human plasmin catalytic domain. Herein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.

Said plasminogen variant, plasmin variant, or plasmin derivative according to the invention may alternatively be one wherein:

-   (i) if the mutation of said at least one internal amino acid at     position P is the mutation of the lysine at position 137 of the     human plasmin catalytic domain (which is amino acid position 698     relative to human Glu-plasminogen) into an amino acid rendering the     peptide bond between amino acids 137 and 138 resistant or more     resistant to autoproteolysis, said plasminogen variant, plasmin     variant or plasmin derivative comprises an intact activation site at     amino acid positions 561 and 562 (relative to human     Glu-plasminogen), and, when amino acids at position 536 and 541     (relative to human Glu-plasminogen) outside the catalytic domain are     present, said amino acids are the wild-type cysteines, or -   (ii) if the mutation of said at least one internal amino acid at     position P is the mutation of the arginine at position 158 of the     human plasmin catalytic domain (which is amino acid position 719     relative to human Glu-plasminogen) into an alanine or glutamate,     then at least one other internal amino acid of the human plasmin     catalytic domain at a position P′ of which the peptide bond with     internal amino acid at position P′+1 is prone to autoproteolysis is     mutated into an amino acid of which the peptide bond with internal     amino acid at position P′+1 is less or not prone to autoproteolysis.

The variants described in (i) and (ii) above may optionally further comprise a mutation of the internal amino acid at position 147 of the human catalytic domain or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.

In any of the above-described plasminogen variants, plasmin variants, or plasmin derivatives said lysine at position 137 of the human catalytic domain, or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, may be mutated into an amino acid of the groups of hydrophobic aliphatic amino acids, hydrophobic aromatic amino acids, hydrophilic acidic amino acids, hydrophilic basic amino acids other than lysine, moderately hydrophobic aromatic amino acids, and moderately hydrophobic aliphatic amino acids. In particular, said lysine may e.g. be mutated into an amino acid chosen from Ala, Glu, Phe, H is, Ile, Met, Gln or Arg.

In any of the above-described plasminogen variants, plasmin variants, or plasmin derivatives said lysine at position 147 of the human catalytic domain, or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, may be mutated into an amino acid of the groups of hydrophobic aliphatic amino acids, hydrophobic aromatic amino acids, hydrophilic acidic amino acids, hydrophilic basic amino acids other than lysine, moderately hydrophobic aromatic amino acids, and moderately hydrophobic aliphatic amino acids. In particular, said lysine may e.g. be mutated into an amino acid chosen from Ala, Glu, Gln, H is, Ile or Phe.

In any of the above-described plasminogen variants, plasmin variants, or plasmin derivatives said arginine at position 158 of the human catalytic domain, or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, may be mutated into an amino acid of the groups of hydrophobic aliphatic amino acids, hydrophobic aromatic amino acids, hydrophilic acidic amino acids, hydrophilic basic amino acids, moderately hydrophobic aromatic amino acids, and moderately hydrophobic aliphatic amino acids. In particular, said arginine may e.g. be mutated into an amino acid chosen from Ala, Glu, Gln, Ile, Phe or His.

“Plasmin”, also known as fibrinolysin or lysofibrin, is a serine-type protease which results from the activation of the zymogen plasminogen. Activation is the result of a proteolytic cleavage between amino acids 561 and 562 (numbering relative to human Glu-plasminogen). Plasmin carries a heavy chain comprising 5 kringle domains and a light chain comprising the catalytic domain. Plasminogen can be enriched from blood plasma, e.g., via lysine affinity-chromatography (Deutsch & Mertz, 1970, Science 170, 1095-1096). Truncation of the plasmin molecule (outside and/or inside the plasmin catalytic domain) is possible as long as the catalytic domain remains functional, such truncation thus results in the formation of a “proteolytically active derivative” of plasmin. As such, one or more of the 5 kringle domains can be deleted wholly or partially. Truncated plasmins lacking one or more kringle domains and/or lacking parts of one or more kringle domains therefore are envisaged by the current invention as examples of proteolytically active derivatives of plasmin Examples of truncated variants of plasmin include, but are not limited to, “midiplasmin”, “miniplasmin”, “microplasmin”, and “delta-plasmin”. Midiplasmin is basically lacking kringle domains 1 to 3 (e.g. Christensen et al., 1995, Biochem J 305, 97-102). Miniplasmin was originally obtained by limited digestion of plasmin with elastase and is basically lacking kringle domains 1 to 4 (e.g. Christensen et al., 1979, Biochim Biophys

Acta 567, 472-481; Powell & Castellino, 1980, J Biol Chem 255, 5329). Miniplasmin has subsequently been produced recombinantly (WO 2002/050290). Microplasmin was originally obtained by incubation of plasmin at elevated pH and is basically lacking all kringle domains (e.g. WO 89/01336). Whereas the microplasmin obtained from incubation of plasmin at elevated pH is containing the 30-31 carboxy-terminal amino acids of the heavy chain, a recombinantly produced microplasmin variant is containing the 19 carboxy-terminal amino acids of the heavy chain (WO 2002/050290). Delta-plasmin is a recombinant version of plasmin in which kringle domain 1 is linked directly with the catalytic domain (WO 2005/105990). The above described truncated variants of plasmin are obtained by activation of “midiplasminogen”, “miniplasminogen”, “microplasminogen” and “delta-plasminogen”, respectively. In order to be activatable, a truncated plasminogen needs to comprise a minimum number of amino acids of the linker between the kringle 5 domain and the catalytic domain (see, e.g., Wang et al., 1995, Protein Science 4, 1758-1767). In the context of the present invention it may be desired that the plasminogen comprises an “intact activation site”, which implies that at least amino acids 561 and 562 (relative to human Glu-plasminogen; or the corresponding amino acids in non-human plasminogen) are such that activation/conversion of plasminogen to plasmin can occur, albeit possibly with different kinetics, as it occurs in wild-type plasmin As alternative to plasmin or an active truncated variant thereof, an activatable plasminogen or a truncated variant thereof can be used in the context of the current invention (see, e.g. EP 0480906; U.S. Pat. No. 5,304,383; EP 0631786; U.S. Pat. No. 5,520,912; U.S. Pat. No. 5,597,800; U.S. Pat. No. 5,776,452). “Plasminogen” refers to any form of plasminogen e.g. Glu-plasminogen or Lys-plasminogen (starting with Arg at position 68 or Lys at positions 77 or 78). When using activatable plasminogen or an activatable truncated variant thereof, the activation to plasmin may be delayed and will typically occur after contacting it with an organ, tissue or body fluid, i.e. after administration to a subject. In yet another alternative, the plasmin or an active truncated variant thereof can be substituted in the context of the current invention for an activatable plasminogen or an activatable truncated variant thereof in conjunction with a plasminogen activator (such as tissue plasminogen activator (tPA), urokinase, streptokinase or staphylokinase, or any variant thereof; see, e.g. U.S. Pat. No. 6,733,750; U.S. Pat. No. 6,585,972; U.S. Pat. No. 6,899,877; WO 03/33019). In yet a further alternative, a mixture of any of (i) plasmin or derivative thereof, (ii) activatable plasminogen or an activatable derivative thereof, and, optionally (iii) a plasminogen activator can be used in the context of the current invention (see, e.g. US 2004/0081643). In order to ensure stability of the plasmin (or plasminogen), it will generally be stored at lowered temperatures (e.g. +4 degrees Celsius or −20 degrees Celsius). The storage composition may be a stabilizing composition such as a low pH composition (pH 4 or lower; obtained by e.g. 1 mM to 250 mM of an acid such as citric acid, see, e.g. Castellino & Sodetz, 1976, Methods Enzymol 45, 273-286; WO 01/36608; WO 01/36609; WO 01/36611) or a high glycerol content composition (30-50% v/v, e.g., Castellino & Sodetz, 1976, Methods Enzymol 45, 273-286), alternatively in or in conjunction with one or more further stabilizer compositions comprising e.g. an amino acid (e.g. lysine or an analogue thereof such as EACA or tranexamic acid), a sugar (e.g. mannitol) or any stabilizer as known in the art (e.g. dipeptides, WO 97/01631). Further included in the genus “plasmin” is any active derivative thereof (or of an active truncated plasmin variant), or similar derivative of activatable plasminogen (or of activatable truncated variant thereof). Such derivates include e.g. labeled plasmin or plasminogen (or truncated variants thereof) such as Tc⁹⁹-labeled plasmin (Deacon et al., 1980, Br J Radiol 53, 673-677) or pegylated or acylated plasmin or plasminogen (or truncated variants thereof; EP 9879, WO 93/15189). Any other label (radioactive, fluorescent, etc.) may also be used to produce a plasmin or plasminogen derivative. Said derivatives further include hybrid or chimeric plasmin or plasminogen molecules comprising e.g. a truncated plasmin or plasminogen according to the invention fused with e.g. a fibrin-binding molecule (such as kringle 2 of tPA, an apolipoprotein kringle, the finger domain of tPA or fibronectin or the Fab domain of a fibrin-binding antibody).

Comparison of the autoproteolytic resistance (i.e. stability) of wild-type plasmin and of plasmin variants or plasmin derivatives according to the invention can be performed in a similar way as as for comparing proteolytic activity, e.g., in a chromogenic activity assay or a biological substrate assay based on e.g. fibrin, fibrinogen or fibronectin.

In order to determine autoproteolytic resistance, the autolysis rate constant can be determined. It is envisaged that the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be characterized by an autolysis rate constant that is at least 5%, or at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 75%, 80%, 90%, 95%, 99% or 99.5% lower than the autolysis rate constant of wild-type plasmin, or, alternatively, by an autolysis rate constant that is at most 95%, or at most 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 75%, 80%, or 90% of the autolysis rate constant of wild-type plasmin. In order to determine the indicated percentage, the calculation can be done based on the absolute autolysis rate constant numbers. For example, wild-type microplasmin has an autolysis rate constant of 230 M⁻¹s⁻¹, whereas the microplasmin variant K137M has an autolysis rate constant of 1 M⁻¹s⁻¹ (see Example 3/Table 3). The autolysis rate constant of the K137M variant therefore is 0.43% of the autolysis rate constant of wild-type microplasmin

Further, any of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or derivatives of any of said plasmins may retain proteolytic activity different (higher or lower) from the proteolytic activity of wild-type plasmin, such as determined with e.g. a chromogenic activity assay or a biological substrate assay based on e.g. fibrin, fibrinogen, fibronectin, gelatin, laminin or collagen.

The proteolytic activities of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be compared to the proteolytic activity of wild-type plasmin by means of the catalytic constant k_(cat) which is a measure of the number of substrate molecule each enzyme site converts to product per unit time. Thus, any of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be characterized by a k_(cat) value which is in the range of +100% to −90%, or +50% to −50% of the k_(cat) value of wild-type plasmin, i.e., characterized by a k_(cat) value in the range of 10% to 200%, or 50% to 150% of the k_(cat) value of wild-type plasmin. In order to determine the indicated percentage, the calculation is done on the absolute k_(cat) numbers. For example, wild-type microplasmin has a k_(cat) of 46 s⁻¹, whereas the microplasmin variant K137M has a k_(cat) of 36s⁻¹ (see Example 4/Table 3). The k_(cat) of the K137M variant therefore is 78.3% of the k_(cat) of wild-type microplasmin

Another way of comparing proteolytic activity of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention to proteolytic activity of wild-type plasmin includes comparing k_(cat)/K_(m) (Table 3). An up to 1000-times or up to 500-times lower k_(cat)/K_(m) of a plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention compared to the k_(cat)/K_(m) of wild-type plasmin can still be acceptable (see further).

Further, any of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be characterized by the combination of the above-defined autolysis rate constant and catalytic constant k_(cat).

Alternatively, any of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be compared to wild-type plasmin by combining autolytic rate constant data and k_(cat)/K_(m) data. For example, a plasmin variant with a 20-times lower autolytic rate constant compared to wild-type plasmin, and with a 10-times lower k_(cat)/K_(m) compared to wild-type plasmin will be 2-times better than the wild-type plasmin. Obviously depending on the ultimate use, a very stable plasmin (i.e. no or nearly no autoproteolytic degradation) with low proteolytic activity may be highly desired, e.g., in cases where low but prolonged plasmin activity is desired or even required to achieve the intended clinical effect. Such highly stable plasmin variants with low proteolytic activity would as such virtually equal slow-release formulations without the real need to actually use a slow-release carrier or adjuvant.

Yet another alternative to compare any of the plasmin variants according to the invention, including the plasmins obtained from the plasminogen variants according to the invention, or any of the plasmin derivatives according to the invention may be compared to wild-type plasmin by combining autolytic rate constant data and k_(cat) data.

Obviously, for any comparative measurements such as described above it is desirable to compare plasmin variants with their closest wild-type plasmin, e.g., to compare a microplasmin variant with wild-type microplasmin, or a miniplasmin variant with wild-type miniplasmin. Furthermore obvious, for any activity measurement, a reversibly inactivated derivative of a plasmin variant according to the invention should first be activated by removing the cause of reversible inactivation (e.g. acylation or non-optimal pH).

Any of the plasminogen variants according to the invention or plasmins obtained therefrom, of the plasmin variants according to the invention may be Glu-plasminogen of Glu-plasmin, Lys-plasminogen or Lys-plasmin, midiplasminogen or midiplasmin, miniplasminogen or miniplasmin, microplasminogen or microplasmin, deltaplasminogen or deltaplasmin

Many assays exist to determine whether or not a plasmin species is proteolytically active. Easy and straightforward assays are based on the digestion of a chromogenic substrate by plasmin present in a sample; chromogenic substrates include S-2403 (Glu-Phe-Lys-pNA) and S-2251 (Val-Leu-Lys-pNA) which release p-nitroaniline (pNA) upon proteolytic cleavage. The amount of pNA formed can be measured by light absorbance at 405 nm. An alternative assay for determining plasmin activity is a potentiometric assay. Colorimetric (using a chromogenic substrate) and potentiometric assays are described in e.g., Castellino & Sodetz (1976, Methods Enzymol 45, 273-286). A further alternative assay for determining plasmin activity is a caseinolytic assay (e.g., Robbins & Summaria, 1970, Methods Enzymol 19, 184-199; Ruyssen & Lauwers, 1978, Chapter IX—Plasmin, In “Pharmaceutical Enzymes”, Story-Scientia, Gent, Belgium, pp. 123-131). Yet another alternative assay for determining plasmin activity is a fibrinolytic assay (e.g., Astrup & Mullertz, 1952, Arch Biochem Biophys 40, 346-351). Further activity assays could be easily designed using other protein substrates. Clearly, such assays may also be used to follow disappearance of plasmin proteolytic activity over time due to autoproteolytic degradation of the enzyme. As an alternative for assessing stability of a plasmin variant or any active truncated variant or derivative thereof of the current invention, said plasmin variant may be incubated in the presence of wild-type plasmin and the resistance of the plasmin variant to digestion by wild-type plasmin can be monitored.

The use of plasmin in the removal of necrotic elements or debris from lesions, wounds, ulcerating wounds (such as ulcerating stitched wounds) etc. has been described in e.g. U.S. Pat. No. 3,208,908. Similarly, topical application of plasmin-comprising therapeutic preparations for the treatment of burns was disclosed in e.g. U.S. Pat. No. 4,122,158. Debridement refers to the removal of dead, damaged and/or infected tissue in order to improve or increase the healing of remaining healthy tissue. Such removal may be obtained by surgical, mechanical or chemical means, or by means of certain species of live maggots that selectively eat necrotic tissue (maggot therapy). Debridement may also be performed using enzymes or may be assisted by enzymes, a process referred to as enzymatic debridement. Debridement is an important aspect in the healing process of burns and other serious wounds and it is used as well in the treatment of some types of snake bites. The application of plasmin (or of any variant or derivative thereof or alternative therefore as described above) in enzymatic debridement (alone or in combination with other types of debridement) is particularly useful in promoting or facilitating wound healing and as an adjunct in surgical procedures such as skin grafting.

A more commonly known use of plasmin (or of any variant or derivative thereof or alternative therefore as described above) relates in general terms to the treatment of (a) pathological deposit(s) of fibrin. Fibrin deposits can result from a wide variety of pathological situations in the body. For example, fibrin-containing blood clots can form in vessels in tissue resulting in deep vein, coronary artery, cerebral artery or retinal vein occlusion or thrombosis. Small accumulations of fibrin precede, and may provide, warning of impending catastrophic thrombosis. Examples include unstable angina pectoris, which is considered a warning of impending coronary thrombosis and transient ischemic attacks, which may precede strokes. Fibrin is furthermore frequently deposited in tissue in association with inflammation associated with many disease processes including infection, autoimmune disease and cancer. Another situation where fibrin is deposited is around abscesses caused by infection with microorganisms. Fibrin deposits are furthermore frequently found associated with certain solid tumors. Fibrin deposition may also occur during the healing of any type of wound. Yet another situation of fibrin deposition is the accumulation of fibrin in a retinal vein, which can lead to retinal degeneration, disturbed vision or even loss of vision. The term pathological fibrin deposit further encompasses such deposits as formed or as present in or at the tip of a catheter, catheter device or other implant such as prosthetic vessels and grafts of synthetic, human or animal origin and effectively blocked by an occlusion comprising fibrin. The term “catheter device” refers to any catheter or tube-like device that may enter the body, including arterial catheters, cardiac catheters, central venous catheters, intravenous catheters, peripherally inserted central catheters, pulmonary artery catheters, tunneled central venous catheters and arterio-venous shunts.

Among the various factors encouraging the process of thrombosis, i.e. the formation of a thrombus or hemostatic plug, are: (1) damage to the endothelial cell lining of the affected blood vessel, (2) an increase in the clotting properties of the blood, and (3) stagnation of blood in the affected blood vessel. Thrombosis can start as a very small lump attached to the damaged part of the blood vessel lining. Its presence encourages further thrombosis to occur, and has the effect of causing a slow-down of blood flow by reducing the inner diameter of the vessel. Further growth of the initially small thrombus often leads to total or almost total blockage of the affected blood vessel. If thrombosis takes place in one of the arteries, the tissues supplied by that artery may be deprived of oxygen and nutrition, causing damage or death of the tissue (gangrene). The severity of the damage depends upon the position and size of the thrombosis, the speed at which it grows and whether the affected area has only one artery or is supplied by collateral blood vessels. If the vessel to a vital organ is affected, e.g. the heart or the brain, the person may be severely crippled or die. Sometimes a thrombus may contain infective organisms such as bacteria, and septic thrombosis may occur, with the formation of pus and infection of the surrounding tissues.

Further uses of plasmin (or of any variant or derivative thereof or alternative therefore as described above) include the reduction of the level of circulating fibrinogen (e.g. WO 93/07893) and its use as an α2-antiplasmin inhibitor (reported to reduce the size of cerebral infarct after ischemic stroke; WO 00/18436).

Yet another use of plasmin (or of any variant or derivative thereof or alternative therefore as described above) is related to the induction of posterior vitreous detachment (PVD) and/or vitreous liquefaction in the eye as an alternative for or as adjunct to mechanical vitrectomy (WO 2004/052228; U.S. Pat. No. 6,733,750; U.S. Pat. No. 6,585,972; U.S. Pat. No. 6,899,877; WO 03/33019; WO 2006/122249; WO 2007/047874; U.S. Pat. No. 5,304,118; US 2006/0024349; US 2003/0147877). Vitrectomy and/or vitreous liquefaction is of benefit for a number of eye conditions such as vitreous floaters (motile debris/deposits of vitreous within the normally transparent vitreous humour which can impair vision), retinal detachment (a blinding condition which may be caused by vitreal traction), macular pucker (scar tissue on macula; macula is required for sharp, central vision; macular pucker is also known as epi- or preretinal membrane, cellophane maculopathy, retina wrinkle, surface wrinkling retinopathy, premacular fibrosis, or internal limiting membrane disease), diabetic retinopathy (proliferative or non-proliferative) which may result in vitreal hemorrhage and/or formation of fibrous scar tissue on the retina (which may cause retinal detachment), macular holes (hole in macula causing a blind spot and caused by vitreal traction, injury or a traumatic event), vitreous hemorrhage (caused by diabetic retinopathy, injuries, retinal detachment or retinal tears, subarachnoidal bleedings (Terson syndrome), or blocked vessels), subhyaloid hemorrhage (bleeding under the hyaloid membrane enveloping the vitreous), macular edema (deposition of fluid and protein on or under the macula of the eye) and macular degeneration (starting with the formation of drusen; occurs in dry and wet form; if correlated with age coined age-related macular degeneration). Other eye-applications of plasmin include the maintenance or rescue of a filtering bleb after trabeculectomy surgery (performed to reduce intra-ocular pressure), see e.g. WO 2009/073457.

Another further use of plasmin (or of any variant or derivative thereof or alternative therefore as described above) resides in diagnosis, more particularly appropriately labeled (e.g. Tc⁹⁹-labeled, see above) plasmin (or any variant or derivative thereof or alternative therefore as described above) may be applied for detecting pathological fibrin deposits. When applying a truncated plasmin or plasminogen variant according to the current invention in such diagnosis, care should be taken that said variant still comprises a fibrin-binding site (whether or not from plasmin itself or added to e.g. the plasmin catalytic domain by creating a hybrid molecule).

The plasmin or any variant or derivative thereof or alternative therefore according to the invention may be stored in a pharmaceutically acceptable carrier, diluent or adjuvant. Such carrier, diluent or adjuvant may consist of or comprise an acidic low buffer such as 1-100 mM acetate or citrate. When acidic, the pharmaceutically acceptable carrier, diluent or adjuvant may have a pH of 2.5 to 4.0, such as at a pH of 3.0 to 3.5, or such as a pH of 3.1. Useful acidic compounds include acetic acid, citric acid, hydrochloric acid, lactic acid, malic acid, tartaric acid or benzoic acid. Formic acid may be used but care should be taken that this compound is not inducing proteolytic cleavage at the C-terminus of Asp-residues. The pharmaceutically acceptable carrier, diluent or adjuvant, acidic or neutral, may comprise one or more amino acids such as serine, threonine, methionine, glutamine, glycine, isoleucine, valine, alanine, aspartic acid, lysine, histidine or any derivatives or analogues thereof. The pharmaceutically acceptable carrier, diluent or adjuvant may comprise a carbohydrate such as a monosaccharide, disaccharide, polysaccharide or polyhydric alcohol. Examples include sugars such as sucrose, glucose, fructose, lactose, trehalose, maltose and mannose, sugar alcohols such as sorbitol and mannitol and polysaccharides such as dextrins, dextrans, glycogen, starches and celluloses. The pharmaceutically acceptable carrier, diluent or adjuvant may comprise compounds such as glycerol, niacinamide, glucosamine, thiamine, citrulline, inorganic salts (such as sodium chloride, potassium chloride, magnesium chloride, calcium chloride), benzyl alcohol or benzoic acid. The pharmaceutically acceptable carrier, diluents or adjuvant may comprise compounds such as ε-aminocaproic acid (EACA) and/or tranexamic acid (see also above & Background section). Some of these compounds may be used as stabilizer of a plasmin or any variant or derivative thereof or alternative therefore as described above.

In view of the above, another aspect of the invention relates to the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or a combination of any thereof for use as a medicament.

A further aspect of the invention relates to compositions comprising the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or a combination of any thereof, and at least one of a pharmaceutically acceptable diluent, carrier or adjuvant. In a further embodiment, said composition may additionally comprise at least one of an anticoagulant, a further thrombolytic agent, an anti-inflammatory agent, an antiviral agent, an antibacterial agent, an antifungal agent, an anti-angiogenic agent, an anti-mitotic agent, an antihistamine or an anaesthetic.

In an embodiment to the above-described two aspects of the invention, the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or of a combination of any thereof, or the composition according to the invention may be used in any clinically relevant setting such as for treating a pathological fibrin deposit, for inducing posterior vitreous detachment in the eye, for inducing liquefaction of the vitreous in the eye, as adjunct to and facilitating vitrectomy in the eye, for inducing posterior vitreous detachment, for resolving vitreomacular adhesion, for closing macular holes, for enzymatic debridement, for reducing circulating fibrinogen, for reducing α2-antiplasmin levels, or in conjunction with trabeculectomy.

In another embodiment to the above-described two aspects of the invention, the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or of a combination of any thereof, or the composition according to the invention may be used for prophylactic purposes or in methods for prophylactic treatment. Prophylactic uses include reducing the risk of development of a pathological fibrin deposit in a mammal having an increased risk of developing it (such as an obese mammal, a mammal not doing sufficient physical exercise or a mammal scheduled to undergo a major surgical event or operation). Other prophylactic uses include the induction of posterior vitreous detachment and/or vitreous liquefaction in an apparent healthy eye of a mammal of which the companion eye is/was diagnosed to require induction of posterior vitreous detachment and/or vitreous liquefaction.

Alternatively, the invention relates to methods for treating, dissolving, loosening, macerating, lysing, inducing or promoting lysis of a pathological fibrin deposit in a subject, said methods comprising contacting said fibrin deposit with an effective amount of the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or of a combination of any thereof, said contacting resulting in the treatment, dissolution, loosening, maceration, lysis, or induction or promotion of lysis of said pathological fibrin deposit.

The invention further relates to methods for inducing posterior vitreous detachment in the eye and/or for inducing liquefaction of the vitreous in the eye, or for facilitating surgical vitrectomy in the eye in a subject, said methods comprising contacting an eye of said subject in need of such treatment with an effective amount of the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention or of a combination of any thereof, said contacting resulting in the induction of said posterior vitreous detachment and/or of said liquefaction of the vitreous, or in the facilitation of said surgical vitrectomy.

The invention also relates to methods for enzymatic debridement of injured tissue of a subject, said method comprising contacting said injured tissue with an effective amount of the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or of a combination of any thereof, said contacting resulting in said enzymatic debridement of said injured tissue.

Other methods of the invention are treating or preventing any other clinically relevant indication, including methods for reducing circulating fibrinogen, or for reducing α2-antiplasmin levels in a subject, said methods comprising contacting a subject in need of such treatment with an effective amount of the isolated plasminogen, plasmin, or any variant or derivative thereof or alternative therefore according to the invention, or of a combination of any thereof, said contacting resulting in said reduction of circulating fibrinogen or of said α2-antiplasmin levels.

In general, the medicament or composition of the invention comprising a plasmin (or any variant or derivative thereof or alternative therefore) according to the invention may, depending on its ultimate use and mode of administration, comprise one or more further active ingredients such as an anticoagulant, a further thrombolytic agent, an anti-inflammatory agent, an antiviral agent, an antibacterial agent, an antifungal agent, an anti-angiogenic agent, an anti-mitotic agent, an antihistamine or anesthetic.

“Anticoagulants” include hirudins, heparins, coumarins, low-molecular weight heparin, thrombin inhibitors, platelet inhibitors, platelet aggregation inhibitors, coagulation factor inhibitors, anti-fibrin antibodies and factor VIII-inhibitors (such as those described in WO 01/04269 and WO 2005/016455).

“Thrombolytic agents” include wild-type plasmin, wild-type plasminogen, urokinase, streptokinase, tissue-type plasminogen activator (tPA or alteplase), urokinase-type plasminogen activator (uPA) and staphylokinase or any variant or derivative of any thereof such as APSAC (anisoylated plasminogen streptokinase activator complex), reteplase, tenecteplase, scuPA (single chain uPA), or a combination of any thereof.

“Anti-inflammatory agents” include steroids (e.g. prednisolone, methylprednisolone, cortisone, hydrocortisone, prednisone, triamcinolone, dexamethasone) and non-steroidal anti-inflammatory agents (NSAIDs; e.g. acetaminophren, ibuprofen, aspirin).

“Antiviral agents” include trifluridine, vidarabine, acyclovir, valacyclovir, famciclovir, and doxuridine.

“Antibacterial agents” or antibiotics include ampicillin, penicillin, tetracycline, oxytetracycline, framycetin, gatifloxacin, gentamicin, tobramycin, bacitracin, neomycin and polymyxin.

“Anti-mycotic/fungistatic/antifungal agents” include fluconazole, amphotericin, clotrimazole, econazole, itraconazole, miconazole, 5-fluorocytosine, ketoconazole and natamycin.

“Anti-angiogenic agents” include antibodies (or fragments thereof) such as anti-VEGF (vascular endothelial growth factor) or anti-P1GF (placental growth factor) antibodies and agents such as macugen (pegaptanib sodium), trypthophanyl-tRNA synthetase (TrpRS), anecortave acetate, combrestatin A4 prodrug, AdPEDF (adenovector capable of expressing pigment epithelium-derived factor), VEGF-trap, inhibitor of VEGF receptor-2, inhibitors of VEGF, P1GF or TGF-13, Sirolimus (rapamycin) and endostatin.

“Anti-mitotic agents” include mitomycin C and 5-fluorouracyl.

“Antihistamine” includes ketitofen fumarate and pheniramine maleate.

“Anesthetics” include benzocaine, butamben, dibucaine, lidocaine, oxybuprocaine, pramoxine, proparacaine, proxymetacaine, tetracaine and amethocaine.

“Contacting”, when used herein, means any mode of administration that results in interaction between a composition such as a medicament and the tissue, body fluid, organ, organism, etc. with which said composition is contacted. The interaction between the composition and the tissue, body fluid, organ, organism, etc can occur starting immediately or nearly immediately with the administration of the composition, can occur over an extended time period (starting immediately or nearly immediately with the administration of the composition), or can be delayed relative to the time of administration of the composition.

Any method of contacting a pathological fibrin deposit that provides (either immediately, delayed or over an extended time period) an effective amount of a plasmin (or any variant or derivative thereof or alternative therefore) to such fibrin deposit can be utilized. If such fibrin deposit is associated with a blood clot, the plasmin (or any variant or derivative thereof or alternative therefore) can be delivered intra-arterially, intravenously, or locally (within short distance of the clot or even in the clot) by means of injection and/or infusion and/or a catheter.

When using plasmin (or any variant or derivative thereof or alternative therefore) in enzymatic debridement, it may be included in a gel-like composition capable of being applied topically, or may be applied in liquid form.

Any method of contacting the eye vitreous and/or aqueous humor that provides (either immediately, delayed or over an extended time period) an effective amount of a plasmin (or any variant or derivative thereof or alternative therefore) to the vitreous and/or aqueous humor can be utilized. One method of contacting the vitreous and/or aqueous humor is by one or more intraocular injections directly into the vitreous and/or aqueous humor. Alternatively, said contacting may involve subconjunctival, intramuscular or intravenous injections. A further alternative contacting method involves placing an intra-vitreal implantable device such as OCUSERT® (Alza Corp., Palo Alto, Calif.) or VITRASERT® (Bausch & Lomb Inc., Rochester, N.Y.). Contacting the vitreous and/or aqueous humor with an effective amount of a plasmin (or any variant or derivative thereof or alternative therefore) may be in a continuous fashion using a depot, sustained release formulation or any implantable device suitable thereto.

The term “effective amount” refers to the dosing regimen of the medicament according to the invention, in particular of the active ingredient of the medicament according to the invention, i.e., plasmin or an active truncated variant thereof (or any alternative therefore as described above). The effective amount will generally depend on and will need adjustment to the mode of contacting or administration and the condition to be treated. The effective amount of the medicament, more particular its active ingredient, is the amount required to obtain the desired clinical outcome or therapeutic or prophylactic effect without causing significant or unnecessary toxic effects. To obtain or maintain the effective amount, the medicament may be administered as a single dose or in multiple doses. The effective amount may further vary depending on the severity of the condition that needs to be treated or the expected severity of the condition that needs to be prevented; this may depend on the overall health and physical condition of the patient and usually the treating doctor's or physician's assessment will be required to establish what is the effective amount. The effective amount may further be obtained by a combination of different types of administration. The medicament may be administered as a solution (liquid or semi-liquid, e.g., gel-like or in dispersion or suspension, colloidal, in emulsion, nanoparticle suspension) or as a solid (e.g. tablet, minitablet, hard- or soft-shelled capsules).

For purposes of thrombolysis, plasmin dosage and duration of plasmin therapy will typically depend on the size and location of the blood clot as well as on the size, weight and age of the patient. If a clot is venous, treatment with plasmin may continue for days whereas only hours of plasmin therapy may be required if the clot is arterial. A myocardial infarction may be treated with a short single dose treatment whereas conditions such as thrombophlebitis and pulmonary embolism may require longer multiple dose treatment. Prolonged continuous and/or intermittent thrombolytic plasmin therapy may be applied to treat a coronary occlusion or in case of prophylactic therapy in order to reduce the risk of clot formation in subjects known to have an increased risk to develop clot formation. A further factor influencing plasmin dosage includes the circulating levels plasmin inhibitors such as α2-antiplasmin and/or α2-macroglobulin, the initial level of which being patient-dependent. It may be advisable to adjust the plasmin dosage such that no more than 15% of the total circulating α2-antiplasmin is remaining in order to achieve efficient thrombolytic therapy. For the purpose of inducing thrombolysis, a contacting method delivering a plasmin or any variant or derivative thereof or alternative therefore at a short distance proximal to a thrombus may be advantageous as the exposure to serum inhibitors is reduced. Such contacting method typically involves delivery via a catheter device. For use in thrombolyis, typical plasmin dosages range from 500 microgram/body weight to 10 milligram/kg body weight given as a single bolus or divided over 1 initial bolus injection followed by 1 or more repeat bolus injections. Plasmin may alternatively be administered over an extended time period, e.g. by infusion or by drug delivery micropump. Plasmin dosages for continued administration may range from 1 to 10 mg/kg/hour.

A typical plasmin dosage for inducing posterior vitreous detachment, vitreous liquefaction, clearance of vitreal blood or hemorrhages, or clearance of toxic materials or foreign substances from the vitreous cavity may be in the range of about 0.1 microgram to about 250 microgram per eye per dose, which can be delivered in a diluent or carrier volume of about 50 microliter to about 300 microliter per eye per dose. The diluent or carrier may e.g. be a sterile Balanced Salt Solution (BSS or BSS Plus), a physiologic saline solution or a solution containing 1-10 mM citric acid. In one embodiment plasmin is delivered to the eye in a dose of 125 microgram contained in 0.1 mL diluent or carrier. In the case of vitrectomy, said plasmin may be delivered to the eye 15 to 300 minutes, or 15 to 120 minutes prior to the vitrectomy. When using plasminogen as an alternative source for plasmin (see “plasmin” definition), up to 250 microgram of plasminogen can be introduced per eye and said plasminogen may be accompanied by up to 2000 IU of urokinase or streptokinase as plasminogen activator or by up to 25 microgram of tPA. When used in the eye, plasmin or plasminogen administration may further be accompanied by administration of a gaseous adjuvant such as air, an expanding gas or liquefiable gas, or mixtures thereof, as long as it is non-toxic to the eye. Other suitable gaseous materials include SF6 (sulfur hexafluoride) and perfluorocarbons, such as C2F6 (hexafluoroethane), C3Fs (octafluoropropane), C4Fs (octafluorocyclobutane), oxygen, nitrogen, carbon dioxide, argon, and other inert gases. The volume of the gaseous material that is introduced into the eye can vary depending on the gaseous material, the patient, and the desired result. For example, the volume of air that is injected into the posterior chamber can range from about 0.5 mL to about 0.9 mL. Other gaseous materials, such as SF6 and perfluorocarbon gases can range from about 0.3 mL to 0.5 mL. Preferably, the gaseous material is introduced into the posterior chamber of the eye in an amount sufficient to compress the vitreous against the posterior hyaloid and form a cavity in the vitreous without damaging the eye. In preferred embodiments, the gaseous adjuvant is introduced into the vitreous to form a cavity that fills about 40% to about 60% of the internal volume of the intraocular cavity.

The above recited dosages are indicative values not meant to be limiting in any way. Said dosages furthermore refer to wild-type plasmin or plasminogen or any active or activatable truncated variant thereof. When using a plasmin with increased stability according to the invention (or any variant or derivative thereof or alternative therefore), and depending on the ultimate stability and residual activity of a plasmin according to the invention, dosages may be similar, higher or lower to obtain the same or better overall clinical effect as obtained with wild-type plasmin. Dosage of a plasmin according to the invention may also depend on the rate of inhibition by endogenous inhibitors such as α2-antiplasmin.

In line with the work herein disclosed, the invention further relates to methods for screening for an autoproteolytically stable plasmin variant, said methods comprising the steps of:

-   (i) identifying in the catalytic domain of wild-type plasmin at     least one internal amino acid at position P of which the peptide     bond with internal amino acid at position P+1 is prone to     autoproteolysis, -   (ii) mutating the amino acid at position P identified in (i) into an     amino acid of which the peptide bond with internal amino acid at     position P+1 is less or not prone to autoproteolysis, -   (iii) determining the autoproteolytic stability of the mutant     obtained from (ii), and -   (iv) selecting from (iii) a mutant that is autoproteolytically     stable as the autoproteolytically stable variant.

The invention likewise relates to methods for screening for an autoproteolytically stable plasmin variant, said methods comprising:

-   (i) mutating one or more of the arginine or lysine amino acids at     positions 137, 147 and 158 of the human plasmin catalytic domain, or     of the corresponding arginines or lysines of a non-human plasmin,     into an amino acid different from the natural amino acid, -   (ii) determining the autoproteolytic stability of the mutant     obtained from (i), and -   (iii) selecting from (ii) a mutant that is autoproteolytically     stable as the autoproteolytically stable plasmin variant;     wherein said human plasmin catalytic domain is starting with the     amino acid valine at position 1 which is the same valine amino acid     occurring at position 562 of human Glu-plasminogen.

The above screening methods may further comprise a step wherein the proteolytic activity of the autoproteolytically stable plasmin variant is determined.

Many products including medicines (here to be understood specifically as user-ready active ingredient, i.e. in the final formulation for administration to a patient) and bulk-stored active ingredients of medicines are usually stored for a considerable amount of time prior to use. It is of interest to extend the shelf-life of products as long as possible. With the shelf-life is meant the time during which the product can be used safely and during which the product retains it potent utility, i.e. its activity in the case of a medicine and/or its active ingredient. Typically, the shelf-life is indicated on a product or its package. Once the shelf-life has expired, the safe and potent utility of a product is no longer guaranteed. A further important aspect in storing products is the storage temperature at which the desired shelf-life can be achieved. For example, the shelf-life of a product stored at +4° C. or average refrigerator temperature may amount to 12 months whereas the shelf-life of the same product stored at −20° C. or average freezer temperature may amount to 36 months. Logistically, however, maintaining a cold chain at freezing temperatures, e.g. −20° C., is much more complex, difficult and expensive than maintaining a cold chain at +4° C. Thus, it may still be attractive to have a shorter, but sufficiently long shelf-life combined with the possibility to store a product at +4° C. The present invention offers a solution for extending, enhancing or increasing the shelf-life or long-term storage stability of plasmin or any active fragment or derivative thereof or of a composition comprising plasmin or any active derivative thereof. The solution resides in making available plasmin variants as herein described, said variants having an enhanced stability, which, intrinsically, increases, enhances or extends their shelf-life.

The invention likewise relates to methods for enhancing long-term storage stability of a plasmin-comprising composition, said methods comprising the step of identifying an autoproteolytically stable plasmin variant capable of being stored over a long time without significant loss of proteolytic activity. For determining long-term stability, a plasmin preparation according to the invention is aliquoted and activity measurements are performed repeatedly during the envisaged storage term. If the envisaged storage term is, e.g., 24 months, activity measurements can be performed, e.g. every month. The allowable loss of proteolytic activity at the end of the envisaged storage term will largely depend on the envisaged clinical application but typically may be no more than e.g. 10% to 15%.

The invention furthermore relates to methods for producing a plasminogen variant according to the invention, i.e. for producing a plasminogen comprising in its catalytic domain the mutation of at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to autoproteolysis into an amino acid of which the peptide bond with internal amino acid at position P+1 is less or not prone to autoproteolysis. Such methods include the steps of:

-   (i) introducing in a suitable host cell a nucleic acid encoding a     plasminogen variant according to the invention in a suitable host     cell capable of expressing said plasminogen; -   (ii) growing the host cell obtained in (i) under conditions and     during a time sufficient for expression of said plasminogen in said     host cell; and -   (iii) harvesting the plasminogen expressed in (ii).

Eventually a step (iv) can be added to such methods which includes the purification of the plasminogen harvested in (iii).

Suitable host cells and methods for expression and production are disclosed in e.g. WO 90/13640 (insect cells), WO 2002/050290 and WO 03/066842 (yeast cells), WO 2008/054592 (bacterial cells/refolding process) and WO 2005/078109 (duckweed transgenic plants or transgenic plant cells).

The invention further encompasses methods for producing a plasmin variant according to the invention, i.e. for producing a plasmin comprising in its catalytic domain the mutation of at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to autoproteolysis into an amino acid of which the peptide bond with internal amino acid at position P+1 is less or not prone to autoproteolysis. Such methods generally include the steps of producing a plasminogen according to the invention as described above and further comprise a step of activating the plasminogen according to the invention to a plasmin according to the invention using a suitable plasminogen activator (such as tPA, uPA, urokinase, streptokinase, staphylokinase or any variant thereof). Eventually one or more steps can be added wherein the plasminogen is purified prior to activation, activated plasmin is purified and/or active plasmin is derivatized as described above and/or reversibly inactivated and/or, optionally, brought to suitable storage conditions (such as stabilizing solution, lyophilized and/or low temperature).

The invention also relates to (an) isolated nucleic acid sequence(s) encoding a plasminogen variant or plasmin variant according to the invention. The invention also relates to (a) recombinant vector(s) comprising such nucleic acid. The invention also relates to (a) host cell(s) transformed with such nucleic acid or with such recombinant vector.

EXAMPLES Example 1 Autodegradation of the plasmin catalytic domain and determination of peptide bonds in the plasmin catalytic domain which are sensitive to autoproteolysis

In order to study the mechanisms underlying the auto-inactivation of the proteolytic activity of plasmin, the inventor chose to focus on microplasmin which consists mainly of the catalytic domain of plasmin.

A typical size exclusion chromatography (SEC) profile of large-scale produced microplasmin is shown in FIG. 2. The eluates corresponding to fraction number 5 (pre-peak 1), fraction numbers 7&8 (pre-peak 2), fraction numbers 10-12 (microplasmin peak), and fraction numbers 15&16 (post-peak) were collected and the material therein subjected to N-terminal amino acid sequencing (Edman degradation). The peak eluting around fraction numbers 17-18 corresponds to the buffer peak. SEC was performed on an Amersham Bioscience Superdex 75 10/300 GL column connected to a Waters Alliance HPLC system. The column was equilibrated and eluted with a buffer containing 8 mM Na₂HPO₄, 1.5 mM KH₂PO₄, 3 mM KCl, 0.5 M (NH₄)₂SO₄, pH 7.4. Fifty μL of a 1 mg/mL microplasmin solution (i.e., 50 μg microplasmin) was injected. The eluate was monitored for proteins with UV absorbance detector at 220 nm.

The obtained amino acid sequences are given in Table 2 and correspond to the microplasmin “heavy chain” (starting with amino acids APS, i.e., the 19 C-terminal amino acids of the heavy chain) and light chain (starting with amino acids VVG), and corresponding to two autodegradation products (starting with amino acids EAQ and amino acids VCN). See FIG. 1 for the complete sequence of plasmin(ogen) and indication of heavy- and light-chains and autocleavage sites. The autodegradation products correspond to cleavage of the amide bond C-terminal of Lys 137 and Lys 147, respectively (numbering starting with Val at position 1 of the light chain of plasmin, see FIG. 1).

TABLE 2 N-terminal amino acid sequences of microplasmin and microplasmin autocatalytic degradation products. Sequence SEC-peak 1 2 3 4 5 6 7 8 9 10 pre-peak 1 A P D F D X (C) G K P Q 21.9 mins V V G G X (C) V A H P pre-peak 2 A P S F D X (C) G K P Q 24.4 mins V V G G X (C) V A H P E A Q L P V I E N K V X (C) N R Y E F L N G μP1 peak A P S F D X (C) G K P Q 27.4 mins V V G G X (C) V A H P H post-peak E A Q L P V I E N K 32.7 mins

Microplasmin from large-scale production was subjected to autocatalytic degradation. Microplasmin at a final concentration of 0.6 mg/mL was incubated for 4 hrs at +20° C. at pH 3.1, pH 4.0, pH 5.0, pH 6.0, and pH 7.0 after which the samples were immediately frozen at −70° C. The samples were analyzed by reducing SDS-PAGE, the results of which are shown in FIG. 3 (Coomassie Brilliant Blue stained gel). FIG. 3 illustrates major autocatalytic degradation products of about 15 kDa, about 10 kDa and somewhat smaller than 10 kDa. The observed bands are in agreement with cleavage sites as determined via N-terminal amino acid sequencing (see Table 1).

In another set of experiments, large-scale produced microplasmin (4 mg/mL in 5 mM citric acid, 6 mg/mL mannitol, pH 3,1) was diluted in a neutral-pH buffer, and aliquots collected after various times were analyzed either by SDS-PAGE or western blot. For the SDS-PAGE analysis, the data were obtained by diluting microplasmin in BSS+ (Alcon; containing per mL 7.14 mg NaCl, 0.38 mg KCl, 0.154 mg CaCl₂, 0.2 mg MgCl₂, 0.42 mg Na-phosphate, 2.1 mg NaHCO₃, 0.92 mg glucose and 0.184 mg glutathione disulfide; pH 7.4) at a final concentration of 1.25 mg/mL, with the sample kept at room temperature (FIG. 4A). For the western-blot analysis, microplasmin (final concentration 1.53 μM) was diluted in PBS and incubated at 37° C., and the western blot was developed with a murine anti-microplasmin antibody (FIG. 4B). FIGS. 4A and 4B illustrate the time-dependent degradation of the intact microplasmin and the accumulation of autocatalytic degradation products. Another sample was prepared by diluting the large-scale produced microplasmin 2-fold in 100 mM sodium phosphate, pH 7.2, and the sample was incubated for 30 min at 37° C. Twenty five micrograms of protein were then resolved on a 4-12% polyacrylamide gel. Following Coomassie staining, the bands corresponding to the two degradation fragments were excised, and the peptides were isolated from the gel and submitted to N-terminal sequencing (performed by Eurosequence B. V., Groningen, The Netherlands). The 15 kDa band yielded the sequence expected for the intact catalytic domain (Val-Val-Gly-Gly). The smaller, 10 kDa fragment yielded the sequence Val-Gln-Ser-Thr-Glu-Leu, which identifies the major cleavage site as being between Arg 158 and Val 159. The 10 kDa fragment also yielded a less abundant (<10%), less well resolved sequence (Xaa-Xaa-Asn-Arg-Tyr), which suggests that a minor cleavage site is located C-terminal to Lys 147. All numberings are starting with Val at position 1 of the light chain of plasmin (see FIG. 1). Thus, when subjecting microplasmin to autodegradation at 2 mg/mL, an additional autocatalytic cleavage site between Arg 158 and Val 159 was identified.

As is illustrated in FIG. 5, the kinetics of microplasmin autolysis as assessed by western-blot (circles) follows the loss of microplasmin activity (squares) as assessed by a chromogenic substrate assay (see Example 3). Autolysis data were from the quantification of the band corresponding to the intact microplasmin in FIG. 4B, and from activity data (which were best fitted using a second-order process equation; not shown). From the above described experiments it was concluded that microplasmin autodegradation is responsible for loss of activity, and that the major sites prone to autocatalytic cleavage are between Arg 158 and Val 159, between Lys 147 and Val 148, and between Lys 137 and Glu 138.

Interestingly, the kinetics of inactivation of microplasmin in eye vitreous were very similar to those observed in PBS (FIG. 6A), and western-blot analysis shows that inactivation of microplasmin in eye vitreous also occurs via autolysis (FIG. 6B). For this, microplasmin was diluted in PBS (squares in FIG. 6A) or in porcine eye vitreous (circles in FIG. 6A) to a final concentration of 1.53 μM, and residual concentration of active microplasmin was measured at various time points using the chromogenic substrate Glu-Phe-Lys-pNA. Porcine eye vitreous samples were collected at the indicated times and analyzed by western blot (FIG. 6B) as described above. The arrow indicates the 15-kDa fragment.

Example 2 Construction, expression and purification of plasminogen variants and activation to plasmin Expression Vector

The pPICZaA secretion vector purchased from Invitrogen Corporation (Carlsbad, Calif.) was used to direct expression and secretion of recombinant human microplasminogen in Pichia pastoris.

This vector contains the secretion signal of the Saccharomyces cerevisiae a-factor prepropeptide. A XhoI recognition sequence is present at the COOH-terminus of the α-factor secretion signal, immediately upstream of the Lys-Arg site that is cleaved by Kex2 to remove the secretion signal from the mature protein. This XhoI restriction site may be used to clone the gene of interest flush with the Kex2 cleavage site by synthesizing the gene with the XhoI and Kex2 recognition sites at its 5′ end. The recombinant gene of interest will then be expressed with the native NH₂-terminus. Engineered immediately downstream from the α-factor secretion signal in the pPICZaA vector is a multiple cloning site with recognition sites for the restriction enzymes EcoRI, SfiI, KpnI, SacII and XbaI to facilitate the cloning of heterologous genes.

Gene Synthesis

To improve expression of human microplasminogen in Pichia pastoris, genes encoding the human microplasminogen and variants thereof were synthesized de novo taking into account the preferred codon usage by Pichia pastoris.

To design the codon-optimized gene sequence, the human microplasminogen amino acid sequence (SEQ ID NO:2) was imported in the program Gene Designer which is developed by DNA2.0 (Menlo Park, Calif.) and is freely available on the internet. This sequence was backtranslated into DNA sequence using the Pichia pastoris codon usage table provided with the program. The nucleotide sequence was then checked manually and adjusted to better fit Escherichia coli codon usage. In addition, 6-base pair palindromic sequences and nucleotide repetitions were removed when possible. At the 5′ end, an XhoI restriction site and the Kex2 cleavage site were added and at the 3′ end, an XbaI restriction site was added.

Mutations were introduced in this wild-type microplasminogen sequence in order to change amino acid residues identified as described in Example 1. Adjacent nucleotides were also changed to introduce a unique restriction site, but in this case care was taken to conserve the encoded amino acid sequence.

In a first variant, the lysine at position 137 is substituted by a glutamine. Lys137 is encoded by the codon AAA at positions 478-480. The nucleotides TTGAAA (positions 475-480) were changed into CTGCAG, introducing a PstI site and changing Lys137 into Gln in the microplasminogen protein, while leaving leucine at position 136 unchanged (nucleotide sequence is in SEQ ID NO:4 and the deduced amino acid sequence in SEQ ID NO:5).

In a second variant, the lysine at position 147 is substituted by a histidine. Lys147 is encoded by the codon AAG at positions 508-510. The nucleotides AAGGTT (positions 508-513) were changed into CACGTG, introducing a Pm1I site and changing Lys147 into H is in the microplasminogen protein, while leaving valine at position 148 unchanged (nucleotide sequence is in SEQ ID NO:6 and the deduced amino acid sequence in SEQ ID NO:7).

In the third variant, the arginine at position 158 is substituted by a histidine. Arg158 is encoded by the codon CGT at positions 540-542. The nucleotides TCGTGTT (positions 539-545) were changed into ACACGTG, introducing a Pm1I site and changing Arg158 into H is in the microplasminogen protein, while leaving glycine at position 157 and valine at position 159 unchanged (nucleotide sequence is in SEQ ID NO:8 and the deduced amino acid sequence in SEQ ID NO:9).

In the fourth variant, all of the changes described above are combined substituting lysine at position 137 by glutamine, lysine at position 147 by histidine and arginine at position 158 by histidine (nucleotide sequence is in SEQ ID NO:10 and the deduced amino acid sequence in SEQ ID NO:11).

Microplasminogen variant sequences were synthesized de novo and cloned into the vector pUC57 by Integrated DNA Technologies (Coralville, Iowa).

In other cases, microplasminogen sequences were synthesized and cloned into the vector pPICZaA by DNA2.0 (Menko Park, Calif.) using the same cloning strategy.

In yet other cases, microplasminogen variants were obtained after site-directed mutagenesis on expression vectors made as described above using the QuikChange II Site Directed Mutagenesis Kit from Stratagene (La Jolla, Calif.). The following primers were used:

Lys137Gln mutation: (sense; SEQ ID NO: 12) CGTTCGGTGCTGGTCTGCTGCAGGAAGCACAATTACCTGTG and (antisense; SEQ ID NO: 13) CACAGGTAATTGTGCTTCCTGCAGCAGACCAGCACCGAACG Lys137Arg mutation: (sense; SEQ ID NO: 14) GGTACGTTCGGTGCTGGTCTGTTGCGTGAAGCACAATTACCTGTGAT TG and (antisense; SEQ ID NO: 15) CAATCACAGGTAATTGTGCTTCACGCAACAGACCAGCACCGAACGTA CC Lys147Ala mutation: (sense; SEQ ID NO: 16) CAATTACCTGTGATTGAGAACGCCGTGTGTAACAGATACGAGTTC and (antisense; SEQ ID NO: 17) GAACTCGTATCTGTTACACACGGCGTTCTCAATCACAGGTAATTG Lys147Glu mutation: (sense; SEQ ID NO: 18) CAATTACCTGTGATTGAGAACGAAGTGTGTAACAGATACGAGTTC and (antisense; SEQ ID NO: 19) GAACTCGTATCTGTTACACACTTCGTTCTCAATCACAGGTAATTG Lys147Gln mutation: (sense; SEQ ID NO: 20) CAATTACCTGTGATTGAGAACCAAGTGTGTAACAGATACGAGTTC and (antisense; SEQ ID NO: 21) GAACTCGTATCTGTTACACACTTGGTTCTCAATCACAGGTAATTG Arg158Ala mutation: (sense; SEQ ID NO: 22) CAGATACGAGTTCCTGAATGGCGCCGTGCAGTCCACTGAGTTGTGTG CAGG and (antisense; SEQ ID NO: 23) CCTGCACACAACTCAGTGGACTGCACGGCGCCATTCAGGAACTCGTA TCTG Arg158Gln mutation: (sense; SEQ ID NO: 24) GATACGAGTTCCTGAATGGTCAGGTTCAGTCCACTGAGTTGTGTG and (antisense; SEQ ID NO: 25) CACACAACTCAGTGGACTGAACCTGACCATTCAGGAACTCGTATC

A full list of the single, double and triple mutants made is given in Table 3 (see further).

Expression Vector Construction for Microplasminogen Variants

Wild-type and variant microplasminogen sequences were digested from the vector pUC57 with XhoI and XbaI, and directionally cloned into the vector pPICZaA. The recipient vector-fragment was prepared by XhoI and XbaI restriction and purified from agarose gel using the Qiaquick gel extraction kit (Qiagen GmbH, Germany) The E. coli strain TOP10 (Invitrogen) was transformed with the ligation mixture and ampicillin resistant clones were selected. Based on restriction analysis, a plasmid clone containing an insert of the expected size was retained for further characterization. Sequence determination of the resulting plasmid clones confirmed the precise insertion of the microplasminogen coding region fused to the α-factor mating signal, as well as the absence of unwanted mutations in the coding region.

Expression of Microplasminogen Variants and Activation to Plasmin

The microplasminogen variants and activated microplasmin variants are obtained by following essentially the procedure as outlined in Example 2 of WO 02/50290.

Prior to activation, the microplasminogen mutants were purified by immuno-affinity directly from the Pichia pastoris supernatants. A murine anti-human microplasmin antibody (raised in Balb/c mice using microplasmin as antigen; produced by hybridoma cell line 7H11A11, available at ThromboGenics N.V.) was coupled on sepharose beads according to the protocol n° 71500015AD from GE Healthcare. Following this protocol, 7.5 mL of immuno-affinity resin were prepared from 45 mg of antibody and packed in a XK 16/20 column. Crude supernatant 200-400 mL (0.2_(l)a filtered from Pichia culture/pH 6.0) was directly loaded on the 7H11A11 affinity column After a wash step (100 mM KH₂PO₄, 0.5M NaCl, pH 6.2, 10 column volumes), the microplasminogen variant was eluted with a 0.2M Glycine-HCl, pH 3.0 buffer. The eluate (fractions 4-6) was neutralized and dialyzed against 25 mM Sodium Phosphate buffer, pH 7.2). The purification of the Lys157Met (K157M) mutant is illustrated in FIG. 7 by means of a chromatogram obtained upon immuno-affinity chromatography (A) and the different eluate fractions were analyzed by SDS-PAGE followed by Coomassie staining (B).

Amino acid sequences and nucleotide sequences of the above described wild-type and variant microplasminogen species are listed hereafter.

SEQ ID NO: 2-Wild-type Human microplasminogen amino acid sequence APSFDCGKPQVEPKKCPGRVVGGCVAHPHSWPWQVSLRTRFGMHFC GGTLISPEWVLTAAHCLEKSPRPSSYKVILGAHQEVNLEPHVQEIE VSRLFLEPTRKDIALLKLSSPAVITDKVIPACLPSPNYVVADRTEC FITGWGETQGTFGAGLLKEAQLPVIENKVCNRYEFLNGRVQSTELC AGHLAGGTDSCQGDSGGPLVCFEKDKYILQGVTSWGLGCARPNKPG VYVRVSRFVTWIEGVMRNN SEQ ID NO: 3-Artificial nucleic acid sequence with optimized codon usage for expression in Pichia. The nucleic acid sequence encodes the wild-type human microplasminogen amino acid sequence of SEQ ID NO: 2 GCACCTTCATTCGACTGTGGTAAGCCTCAGGTCGAACCTAAGAAGT GTCCAGGTCGTGTTGTCGGTGGCTGTGTGGCTCATCCTCATTCTTG GCCTTGGCAAGTGTCTCTTAGAACTAGATTTGGTATGCACTTCTGT GGTGGCACCTTGATCTCACCTGAATGGGTCTTAACCGCAGCTCATT GTCTGGAGAAGTCACCACGTCCATCTTCATACAAGGTCATCCTTGG CGCACATCAGGAAGTCAATCTTGAGCCTCATGTTCAGGAGATCGAA GTCTCTCGTTTGTTCTTGGAACCAACTCGTAAAGACATTGCTCTTC TGAAGCTGTCATCTCCTGCCGTGATTACCGACAAGGTAATTCCTGC CTGCTTGCCTAGTCCTAATTACGTCGTTGCCGACCGTACCGAATGC TTCATTACTGGTTGGGGTGAGACTCAAGGTACGTTCGGTGCTGGTC TGTTGAAAGAAGCACAATTACCTGTGATTGAGAACAAGGTTTGTAA CAGATACGAGTTCCTGAATGGTCGTGTTCAGTCCACTGAGTTGTGT GCAGGTCACCTTGCAGGTGGTACTGATAGTTGTCAAGGTGATTCTG GTGGACCACTGGTGTGCTTCGAGAAGGATAAGTACATCTTACAAGG TGTTACGTCTTGGGGTCTTGGATGTGCTCGTCCTAACAAGCCAGGT GTCTACGTCAGAGTCTCCAGATTCGTAACTTGGATCGAAGGTGTCA TGCGTAACAACTAA SEQ ID NO: 4-Microplasminogen variant with the Lys137Gln substitution (mutated codon in bold italics, restriction sites XhoI, PstI and XbaI underlined) CTCGAGAAAAGAGCACCTTCATTCGACTGTGGTAAGCCTCAGGTCG AACCTAAGAAGTGTCCAGGTCGTGTTGTCGGTGGCTGTGTGGCTCA TCCTCATTCTTGGCCTTGGCAAGTGTCTCTTAGAACTAGATTTGGT ATGCACTTCTGTGGTGGCACCTTGATCTCACCTGAATGGGTCTTAA CCGCAGCTCATTGTCTGGAGAAGTCACCACGTCCATCTTCATACAA GGTCATCCTTGGCGCACATCAGGAAGTCAATCTTGAGCCTCATGTT CAGGAGATCGAAGTCTCTCGTTTGTTCTTGGAACCAACTCGTAAAG ACATTGCTCTTCTGAAGCTGTCATCTCCTGCCGTGATTACCGACAA GGTAATTCCTGCCTGCTTGCCTAGTCCTAATTACGTCGTTGCCGAC CGTACCGAATGCTTCATTACTGGTTGGGGTGAGACTCAAGGTACGT TCGGTGCTGGTCTG

GAAGCACAATTACCTGTGATTGAGAA CAAGGTTTGTAACAGATACGAGTTCCTGAATGGTCGTGTTCAGTCC ACTGAGTTGTGTGCAGGTCACCTTGCAGGTGGTACTGATAGTTGTC AAGGTGATTCTGGTGGACCACTGGTGTGCTTCGAGAAGGATAAGTA CATCTTACAAGGTGTTACGTCTTGGGGTCTTGGATGTGCTCGTCCT AACAAGCCAGGTGTCTACGTCAGAGTCTCCAGATTCGTAACTTGGA TCGAAGGTGTCATGCGTAACAACTAATCTAGA SEQ ID NO: 5-Deduced amino acid sequence of SEQ ID NO: 4 (the underlined N-terminal amino acids “LEKR” are encoded by the introduced XhoI + Kex2 cleavage sites; the introduced amino acid mutation is indicated in bold/ italic and is underlined) LEKRAPSFDCGKPQVEPKKCPGRVVGGCVAHPHSWPWQVSLRTRFG MHFCGGTLISPEWVLTAAHCLEKSPRPSSYKVILGAHQEVNLEPHV QEIEVSRLFLEPTRKDIALLKLSSPAVITDKVIPACLPSPNYVVAD RTECFITGWGETQGTFGAGLL

EAQLPVIENKVCNRYEFLNGRVQS TELCAGHLAGGTDSCQGDSGGPLVCFEKDKYILQGVTSWGLGCARP NKPGVYVRVSRFVTWIEGVMRNN SEQ ID NO: 6-Microplasminogen variant with the Lys147His substitution (mutated codon in bold italics, restriction sites XhoI, PmlI and XbaI underlined) CTCGAGAAAAGAGCACCTTCATTCGACTGTGGTAAGCCTCAGGTCG AACCTAAGAAGTGTCCAGGTCGTGTTGTCGGTGGCTGTGTGGCTCA TCCTCATTCTTGGCCTTGGCAAGTGTCTCTTAGAACTAGATTTGGT ATGCACTTCTGTGGTGGCACCTTGATCTCACCTGAATGGGTCTTAA CCGCAGCTCATTGTCTGGAGAAGTCACCACGTCCATCTTCATACAA GGTCATCCTTGGCGCACATCAGGAAGTCAATCTTGAGCCTCATGTT CAGGAGATCGAAGTCTCTCGTTTGTTCTTGGAACCAACTCGTAAAG ACATTGCTCTTCTGAAGCTGTCATCTCCTGCCGTGATTACCGACAA GGTAATTCCTGCCTGCTTGCCTAGTCCTAATTACGTCGTTGCCGAC CGTACCGAATGCTTCATTACTGGTTGGGGTGAGACTCAAGGTACGT TCGGTGCTGGTCTGTTGAAAGAAGCACAATTACCTGTGATTGAGAA C

TGTAACAGATACGAGTTCCTGAATGGTCGTGTTCAGTCC ACTGAGTTGTGTGCAGGTCACCTTGCAGGTGGTACTGATAGTTGTC AAGGTGATTCTGGTGGACCACTGGTGTGCTTCGAGAAGGATAAGTA CATCTTACAAGGTGTTACGTCTTGGGGTCTTGGATGTGCTCGTCCT AACAAGCCAGGTGTCTACGTCAGAGTCTCCAGATTCGTAACTTGGA TCGAAGGTGTCATGCGTAACAACTAATCTAGA SEQ ID NO: 7-Deduced amino acid sequence of SEQ ID NO: 6 (the underlined N-terminal amino acids “LEKR” are encoded by the introduced XhoI + Kex2 cleavage sites; the imtroduced amino acid mutation is indicated in bold/ italic and is underlined) LEKRAPSFDCGKPQVEPKKCPGRVVGGCVAHPHSWPWQVSLRTRFG MHFCGGTLISPEWVLTAAHCLEKSPRPSSYKVILGAHQEVNLEPHV QEIEVSRLFLEPTRKDIALLKLSSPAVITDKVIPACLPSPNYVVAD RTECFITGWGETQGTFGAGLLKEAQLPVIEN

VCNRYEFLNGRVQS TELCAGHLAGGTDSCQGDSGGPLVCFEKDKYILQGVTSWGLGCARP NKPGVYVRVSRFVTWIEGVMRNN SEQ ID NO: 8-Microplasminogen variant with the Arg158His substitution (mutated codon in bold italics, restriction sites XhoI, PmlI and XbaI underlined) CTCGAGAAAAGAGCACCTTCATTCGACTGTGGTAAGCCTCAGGTCG AACCTAAGAAGTGTCCAGGTCGTGTTGTCGGTGGCTGTGTGGCTCA TCCTCATTCTTGGCCTTGGCAAGTGTCTCTTAGAACTAGATTTGGT ATGCACTTCTGTGGTGGCACCTTGATCTCACCTGAATGGGTCTTAA CCGCAGCTCATTGTCTGGAGAAGTCACCACGTCCATCTTCATACAA GGTCATCCTTGGCGCACATCAGGAAGTCAATCTTGAGCCTCATGTT CAGGAGATCGAAGTCTCTCGTTTGTTCTTGGAACCAACTCGTAAAG ACATTGCTCTTCTGAAGCTGTCATCTCCTGCCGTGATTACCGACAA GGTAATTCCTGCCTGCTTGCCTAGTCCTAATTACGTCGTTGCCGAC CGTACCGAATGCTTCATTACTGGTTGGGGTGAGACTCAAGGTACGT TCGGTGCTGGTCTGTTGAAAGAAGCACAATTACCTGTGATTGAGAA CAAGGTTTGTAACAGATACGAGTTCCTGAATGGA

CAGTCC ACTGAGTTGTGTGCAGGTCACCTTGCAGGTGGTACTGATAGTTGTC AAGGTGATTCTGGTGGACCACTGGTGTGCTTCGAGAAGGATAAGTA CATCTTACAAGGTGTTACGTCTTGGGGTCTTGGATGTGCTCGTCCT AACAAGCCAGGTGTCTACGTCAGAGTCTCCAGATTCGTAACTTGGA TCGAAGGTGTCATGCGTAACAACTAATCTAGA SEQ ID NO: 9-Deduced amino acid sequence of SEQ ID NO: 8 (the underlined N-terminal amino acids “LEKR” are encoded by the introduced XhoI + Kex2 cleavage sites; the introduced amino acid mutation is indicated in bold/ italic and is underlined) LEKRAPSFDCGKPQVEPKKCPGRVVGGCVAHPHSWPWQVSLRTRFG MHFCGGTLISPEWVLTAAHCLEKSPRPSSYKVILGAHQEVNLEPHV QEIEVSRLFLEPTRKDIALLKLSSPAVITDKVIPACLPSPNYVVAD RTECFITGWGETQGTFGAGLLKEAQLPVIENKVCNRYEFLNG

VQS TELCAGHLAGGTDSCQGDSGGPLVCFEKDKYILQGVTSWGLGCARP PNKPGVYVRVSRFVTWIEGVMRNN SEQ ID NO: 10-Microplasminogen variant with the Lys137Gln, Lys147His and Arg158His substitutions (mutated codons in bold italics, restriction sites XhoI, PstI, PmlI and XbaI underlined) CTCGAGAAAAGAGCACCTTCATTCGACTGTGGTAAGCCTCAGGTCG AACCTAAGAAGTGTCCAGGTCGTGTTGTCGGTGGCTGTGTGGCTCA TCCTCATTCTTGGCCTTGGCAAGTGTCTCTTAGAACTAGATTTGGT ATGCACTTCTGTGGTGGCACCTTGATCTCACCTGAATGGGTCTTAA CCGCAGCTCATTGTCTGGAGAAGTCACCACGTCCATCTTCATACAA GGTCATCCTTGGCGCACATCAGGAAGTCAATCTTGAGCCTCATGTT CAGGAGATCGAAGTCTCTCGTTTGTTCTTGGAACCAACTCGTAAAG ACATTGCTCTTCTGAAGCTGTCATCTCCTGCCGTGATTACCGACAA GGTAATTCCTGCCTGCTTGCCTAGTCCTAATTACGTCGTTGCCGAC CGTACCGAATGCTTCATTACTGGTTGGGGTGAGACTCAAGGTACGT TCGGTGCTGGTCTG

GAAGCACAATTACCTGTGATTGAGAA C

TGTAACAGATACGAGTTCCTGAATGGA

CAGTCC ACTGAGTTGTGTGCAGGTCACCTTGCAGGTGGTACTGATAGTTGTC AAGGTGATTCTGGTGGACCACTGGTGTGCTTCGAGAAGGATAAGTA CATCTTACAAGGTGTTACGTCTTGGGGTCTTGGATGTGCTCGTCCT AACAAGCCAGGTGTCTACGTCAGAGTCTCCAGATTCGTAACTTGGA TCGAAGGTGTCATGCGTAACAACTAATCTAGA SEQ ID NO: 11-Deduced amino acid sequence of SEQ ID NO: 10 (the underlined N-terminal amino acids “LEKR” are encoded by the introduced XhoI + Kex2 cleavage sites; the introduced amino acid mutations are indicated in bold/ italic and is underlined) LEKRAPSFDCGKPQVEPKKCPGRVVGGCVAHPHSWPWQVSLRTRFG MHFCGGTLISPEWVLTAAHCLEKSPRPSSYKVILGAHQEVNLEPHV QEIEVSRLFLEPTRKDIALLKLSSPAVITDKVIPACLPSPNYVVAD RTECFITGWGETQGTFGAGLL

EAQLPVIEN

VCNRYEFLNG

VQS TELCAGHLAGGTDSCQGDSGGPLVCFEKDKYILQGVTSWGLGCARP NKPGVYVRVSRFVTWIEGVMRNN

Example 3 Reduced Autoproteolyis of Plasmin Variants Compared to Wild-Type Plasmin

The purified microplasminogen mutants were first converted into the active microplasmin species using recombinant staphylokinase (SAK-SY162) or urokinase (Sigma). Briefly, the microplasminogen mutants (typically 5 to 20 μM in 25 mM sodium phosphate, pH 7.2) were incubated at 37° C. in the presence of staphylokinase (typical microplasminogen/staphylokinase ratio=50/1) or urokinase (typical microplasminogen/urokinase ratio=200), and the appearance of the active microplasmin species was followed by monitoring the hydrolytic activity against the chromogenic substrate S-2403 (used at a concentration of 0.3 mM), as described elsewhere. Once maximal activity was reached, the extent of microplasminogen conversion was assessed by SDS-PAGE and HPLC. Following activation, the autolytic reaction was monitored by measuring the loss of activity in the sample maintained at 37° C. Autolytic degradation was also visualized by SDS-PAGE and HPLC. A typical example of such an experiment is shown in FIGS. 8A-C. The determination of the second-order rate constant for autolysis (k) was determined as follows: (1) the microplasmin peak area in HPLC was used to calculate the molar concentration of the active microplasmin species (by comparison with a standard curve established with purified, wild-type microplasmin) at the end of the activation phase/beginning of the autolytic phase; (2) the loss of activity measured during the autolytic phase was used to calculate for each time point the residual, molar concentration of active microplasmin; (3) the residual microplasmin concentration (in mol/l) was plotted as a function of time (in s), and the data were fitted with Equation 1 by non-linear regression analysis to obtain an autolysis constant k, the value of which is expressed in M⁻¹ s⁻¹.

$\begin{matrix} {\left\lbrack {\mu \; {PL}} \right\rbrack = \frac{\left\lbrack {\mu \; {PL}} \right\rbrack_{0}}{1 + {\left\lbrack {\mu \; {PL}} \right\rbrack_{0} \cdot k \cdot t}}} & {{Equation}\mspace{14mu} 1} \end{matrix}$

In Equation 1, [μPL] is the concentration of microplasmin at any given time and [μPL]₀ is the concentration at t=0. An example of such a curve is shown in FIG. 8D, and the k values measured for various microplasmin mutants are listed in Table 3 (see further).

SAK-SY162 is a variant of the staphylokinase Sak-STAR (Collen et al. 1992; Fibrinolysis 6, 203-213) with the following amino acid substitutions: K35A, E65Q, K74R, E80A, D82A, T90A, E99D, T101S, E108A, K109A, K130T and K135R.

Example 4 Proteolytic Activity of Plasmin Variants Compared to Wild-Type Plasmin

The hydrolytic activity of microplasmin can be followed using the chromogenic substrate Glu-Phe-Lys-pNA (S-2403, Chromogenix, Milano, Italy). Upon hydrolysis of the substrate, the pNA (p-nitroaniline) group is released, which results in an increase in the absorbance at 405 nm. Activity of wild-type microplasmin and microplasmin variants was measured with the help of a Powerwave X (Bio-Tek) plate reader. Assays were performed at 37° C., in 50 mM Tris, 38 mM NaCl, 0.01% Tween 80, pH 7.4.

For the microplasmin variants, the preparations were first activated with staphylokinase or urokinase, and the concentration of the active microplasmin species was determined at the end of the activation phase as described elsewhere. However, in order to prevent subsequent inactivation, the activated samples were stabilized by lowering the pH to ˜3 by addition of 2 volumes of 5 mM citric acid.

The kinetic parameters (k_(cat) & K_(m)) of the microplasmin variants against the chromogenic substrate S-2403 were obtained by measuring initial rates of hydrolysis at various substrate concentrations, and by analysing the data with Equation 2, where [μPL] is the concentration of active microplasmin as measured by HPLC, and [S] is the concentration of S-2403. An example of k_(cat) and K_(m) determination from the measurement of initial rates of hydrolysis is shown in FIG. 9.

$\begin{matrix} {v_{i} = \frac{k_{cat} \cdot \left\lbrack {\mu \; {PL}} \right\rbrack \cdot \lbrack S\rbrack}{K_{m} + \lbrack S\rbrack}} & {{Equation}\mspace{14mu} 2} \end{matrix}$

The k_(cat) and K_(m) values obtained for various microplasmin mutants are listed in Table 3.

TABLE 3 Overview of kinetic parameters (k_(cat) and K_(m)) and autolysis rate constants of wild-type microplasmin and a series of single, double, and triple mutants. Kinetic parameters Autolysis rate constant Mutant k_(cat) (s⁻¹) K_(m) (M) k (M⁻¹s⁻¹) wild-type 46 7.6 × 10⁻⁵ 230 137A 61 1.4 × 10⁻² 3 137E 5 2.2 × 10⁻³ 1 137F 29 4.0 × 10⁻³ 1.6 137H 54 6.0 × 10⁻³ 8 137I ND ND 5 137M 36 4.7 × 10⁻³ 1 137Q 55 3.6 × 10⁻³ 10 137R 39 8.1 × 10⁻³ 3 147A 34 1.3 × 10⁻⁴ 24 147E 35 9.2 × 10⁻⁵ 21 147F 32 1.0 × 10⁻⁴ 122 147H 51 1.3 × 10⁻⁴ 118 147I 36 1.1 × 10⁻⁴ 76 147Q 39 8.5 × 10⁻⁵ 45 158A 32 1.2 × 10⁻⁴ 80 158E 24 1.8 × 10⁻⁴ 86 158F 36 2.2 × 10⁻⁴ 159 158H 59 1.7 × 10⁻⁴ 192 158I 31 2.1 × 10⁻⁴ 66 158Q 29 1.2 × 10⁻⁴ 59 137A147A 64 1.6 × 10⁻² 5 137A147H 40 1.2 × 10⁻² 1 137A158A 36 6.4 × 10⁻³ 1.4 137A158H 30 1.1 × 10⁻² 0.7 137H147H 38 6.2 × 10⁻³ 3 137H158H 40 7.7 × 10⁻³ 2 137Q147H 69   8 × 10⁻³ <0.5 137Q158H 38 3.9 × 10⁻³ <1.3 147A158A 33 7.9 × 10⁻⁵ 26 147A158H 27 1.1 × 10⁻⁴ 57 147H158H 50 1.7 × 10⁻⁴ 163 147H158A 29 1.3 × 10⁻⁴ 30 137A147A158A 46 8.3 × 10⁻³ <0.8 137A147H158H 25 9.1 × 10⁻³ <0.7 137H147A158A 27 3.2 × 10⁻³ <1.2 137H147H158H 34 4.5 × 10⁻³ <0.6 137Q147H158H 45 6.6 × 10⁻³ 1 137R147H158H 30 7.2 × 10⁻³ <4

Example 5 Therapeutic Efficacy of Plasmin Variants in In Vitro or In Vivo Models 5.1 Effect of Plasmin Variants on Cerebral Infarct Size.

The efficacy of the plasmin variants of the invention in reducing cerebral infarct size can be performed in a murine cerebral infarct model such as described in Example 2 of WO 00/18436, or according to Welsh et al. (1987, J Neurochem 49, 846-851). The beneficial effect of wild-type plasmin on cerebral infarct size was demonstrated in Example 5 of WO 00/18436. A similar experiment is performed with any of the plasmin variants of the invention and the beneficial effect of these plasmin variants is measured and compared to the beneficial effect of wild-type plasmin.

5.2 In Vivo Thrombolytic Activity of Plasmin Variants

The rabbit extracorporeal loop thrombolysis model (Example 6 of WO 02/50290; Hotchkiss et al., 1987, Thromb Haemost 58, 107 —Abstract 377), the dog circumflex coronary artery copper coil-induced thrombosis model (Example 8 of WO 02/50290; Bergmann et al., 1983, Science 220, 1181-1183) or the rabbit jugular vein thrombosis model (Collen et al., 1983, J Clin Invest 71, 368-376) can be used to demonstrate in vivo thrombolytic activity of the plasmin variants of the invention. The beneficial effect of wild-type plasmin on thrombolysis was demonstrated with these models as described in Examples 7 and 9 of WO 00/18436 and by Collen et al. (1983). Similar experiments are performed with any of the plasmin variants of the invention and the beneficial effect of these plasmin variants is measured and compared to the beneficial effect of wild-type plasmin.

5.3 In Vitro Thrombolytic Activity of Plasmin Variants

An in vitro model of peripheral arterial occlusion (P AO) is described in Example 6 of WO 01/36609 and the thrombolytic efficacy of wild-type plasmin was demonstrated in this model. A similar experiment is performed with any of the plasmin variants of the invention and the beneficial effect of these plasmin variants on thrombolysis of peripheral arterial occlusions is measured and compared to the beneficial effect of wild-type plasmin.

5.4 Liquefaction of Eye Vitreous and Posterior Vitreous Detachment Induced by Plasmin Variants

Example 5 of WO 2004/052228 discloses an assay for determining the efficacy, as well as the efficacy of microplasmin in liquefying the vitreous in post-mortem pig eyes. Example 6 of WO 2004/052228 discloses an assay for determining the efficacy, as well as the efficacy of microplasmin in inducing posterior vitreous detachment (PVD) in human post-mortem eyes. Induction of vitreous liquefaction and PVD by the plasmin variants of the invention is demonstrated in similar post-mortem models.

5.5 In Vivo PVD Induced by Plasmin Variants

Example 7 of WO 2004/052228 discloses an assay for determining the efficacy, as well as the efficacy of microplasmin in inducing PVD in an in vivo feline model. Induction of PVD by the plasmin variants of the invention is demonstrated in a similar in vivo model. 

1. An isolated plasminogen variant or plasmin obtained from it, or an isolated plasmin variant, or a proteolytically active or reversible inactive derivative of any of said plasmins characterized in that it comprises in its catalytic domain the mutation of at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to autoproteolysis into an amino acid of which the peptide bond with internal amino acid at position P+1 is less prone to autoproteolysis.
 2. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 comprising in its catalytic domain the mutation of at least two internal amino acids at position P and P′ of which the peptide bond with internal amino acids at positions P+1 and P′+1 are prone to autoproteolysis into amino acids of which the peptide bond with internal amino acids at position P+1 and P′+1 is less prone to autoproteolysis
 3. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 wherein said internal amino acids at positions P or P and P′ are lysines or arginines.
 4. The plasminogen, plasmin, or plasmin derivative according to claim 1 wherein said at least one or two internal amino acids at position P or positions P and P′ are one of or two of: (i) lysine at position 137 of the human plasmin catalytic domain, or the corresponding lysine or arginine of a non-human plasmin catalytic domain; (ii) lysine at position 147 of the human plasmin catalytic domain, or the corresponding lysine or arginine of a non-human plasmin catalytic domain; or (iii) arginine at position 158 of the human plasmin catalytic domain, or the corresponding arginine or lysine of a non-human plasmin catalytic domain; wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.
 5. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 wherein said at least one internal amino acid at position P is the lysine at position 147 of the human plasmin catalytic domain, or is the corresponding lysine or arginine of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.
 6. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 5 further comprising a mutation of the internal amino acids at positions 137 and/or 158 of the human catalytic domain or of the corresponding lysines and/or arginines of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.
 7. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 wherein (i) if the mutation of said at least one internal amino acid at position P is the mutation of the lysine at position 137 of the human plasmin catalytic domain (which is amino acid position 698 relative to human Glu-plasminogen) into an amino acid rendering the peptide bond between amino acids 137 and 138 more resistant to autoproteolysis, said plasminogen variant, plasmin variant or plasmin derivative comprises an intact activation site at amino acid positions 561 and 562 (relative to human Glu-plasminogen), and, when amino acids at position 536 and 541 (relative to human Glu-plasminogen) outside the catalytic domain are present, said amino acids are the wild-type cysteines, or (ii) if the mutation of said at least one internal amino acid at position P is the mutation of the arginine at position 158 of the human plasmin catalytic domain (which is amino acid position 719 relative to human Glu-plasminogen) into an alanine or glutamate, then at least one other internal amino acid of the human plasmin catalytic domain at a position P′ of which the peptide bond with internal amino acid at position P′+1 is prone to autoproteolysis is mutated into an amino acid of which the peptide bond with internal amino acid at position P′+1 is less or not prone to autoproteolysis.
 8. The plasminogen variant, plasmin variant, or plasmin derivative according to claim 7 further comprising a mutation of the internal amino acid at position 147 of the human catalytic domain or of the corresponding lysine or arginine of a non-human plasmin catalytic domain, wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.
 9. The plasmin variant or plasmin derivative according to claim 1 further characterized in that it is its autolysis constant is at most 95% of the autolysis constant of wildtype plasmin.
 10. The plasmin variant or plasmin derivative according to claim 1 further characterized in that the catalytic constant k_(cat) is in the range of 10% to 200% of the k_(cat) of wildtype plasmin.
 11. The plasmin variant or plasmin derivative according to claim 1 further characterized in that its autolysis constant is at most 95% of the autolysis constant of wildtype plasmin and its catalytic constant k_(cat) is in the range of 10% to 200% of the k_(cat) of wildtype plasmin.
 12. The isolated plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 wherein said plasminogen or plasmin is Glu-plasminogen or Glu-plasmin, Lys-plasminogen or Lys-plasmin, midiplasminogen or midiplasmin, miniplasminogen or miniplasmin, microplasminogen or microplasmin, deltaplasminogen or deltaplasmin.
 13. (canceled)
 14. A composition comprising the isolated plasminogen variant, plasmin variant, or plasmin derivative according to claim 1, or a combination of any thereof, and at least one of a pharmaceutically acceptable diluent, carrier or adjuvant.
 15. The composition according to claim 14 further comprising at least one of an anticoagulant, a thrombolytic agent, an anti-inflammatory agent, an antiviral agent, an antibacterial agent, an antifungal agent, an anti-angiogenic agent, an anti-mitotic agent, an antihistamine or an anaesthetic.
 16. The isolated plasminogen variant, plasmin variant, or plasmin derivative according to claim 1 for inducing or promoting lysis of a pathological fibrin deposit in a subject, for inducing posterior vitreous detachment in the eye and/or for inducing liquefaction of the vitreous in the eye, or for facilitating surgical vitrectomy in the eye in a subject, for enzymatic debridement of injured tissue of a subject, for reducing circulating fibrinogen in a subject, for reducing α2-antiplasmin levels in a subject, or for reducing the risk of pathological fibrin deposition in a subject. 17-20. (canceled)
 21. A method for screening for an autoproteolytically stable plasmin variant, said method comprising: (i) identifying in the catalytic domain of wild-type plasmin at least one internal amino acid at position P of which the peptide bond with internal amino acid at position P+1 is prone to autoproteolysis, (ii) mutating the amino acid at position P identified in (i) into an amino acid of which the peptide bond with internal amino acid at position P+1 is less prone to autoproteolysis, (iii) determining the autoproteolytic stability of the mutant obtained from (ii), and (iv) selecting from (iii) a mutant that is autoproteolytically stable as the autoproteolytically stable variant.
 22. A method for screening for an autoproteolytically stable plasmin variant, said method comprising: (i) mutating one or more of the arginine or lysine amino acids at positions 137, 147 and 158 of the human plasmin catalytic domain, or of the corresponding arginines or lysines of a non-human plasmin, into an amino acid different from the natural amino acid, (ii) determining the autoproteolytic stability of the mutant obtained from (i), and (iii) selecting from (ii) a mutant that is autoproteolytically stable as the autoproteolytically stable plasmin variant; wherein said human plasmin catalytic domain is starting with the amino acid valine at position 1 which is the same valine amino acid occurring at position 562 of human Glu-plasminogen.
 23. (canceled)
 24. A method for enhancing long-term storage stability of a plasmin-comprising composition, said method comprising the step of identifying an autoproteolytically stable plasmin variant capable of being stored over a long time without significant loss of proteolytic activity.
 25. A method for producing a plasminogen variant according to claim 1, said method including the steps of: (i) introducing a nucleic acid encoding a plasminogen according to claim 1 in a suitable host cell capable of expressing said plasminogen; (ii) growing the host cell obtained in (i) under conditions and during a time sufficient for expression of said plasminogen in said host cell; and (iii) harvesting the plasminogen expressed in (ii).
 26. (canceled)
 27. A method for producing a plasmin variant according to claim 1, said method including the steps of: (i) introducing a nucleic acid encoding a plasminogen according to claim 1 in a suitable host cell capable of expressing said plasminogen; (ii) growing the host cell obtained in (i) under conditions and during a time sufficient for expression of said plasminogen in said host cell; (iii) harvesting the plasminogen expressed in (ii); (iv) activating the plasminogen of (iii) to plasmin. 28-29. (canceled)
 30. The method according to claim 27 wherein the active plasmin is derivatized and/or reversibly inactivated.
 31. An isolated nucleic acid sequence encoding the plasminogen variant or plasmin variant according to claim
 1. 32. A recombinant vector comprising the nucleic acid according to claim
 31. 33. A host cell transformed with the nucleic acid according to claim
 31. 34. A host cell transformed with the vector according to claim
 32. 